Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.32   4.744%   $197.2539   $197.25   $197.25   $197.30  
  Purchase #2 $131.99   8.772%   $143.5682   $143.57   $143.55   $143.60  
  Purchase #3 $245.77   10.768%   $272.2345   $272.23   $272.25   $272.20  
  Purchase #4 $217.27   3.313%   $224.4682   $224.47   $224.45   $224.50  
  Purchase #5 $213.33   4.623%   $223.1922   $223.19   $223.20   $223.20  
  Purchase #6 $120.94   5.785%   $127.9364   $127.94   $127.95   $127.90  
  Purchase #7 $168.50   11.526%   $187.9213   $187.92   $187.90   $187.90  
  7 purchase totals = $1,286.12       $1,376.5747   $1,376.57   $1,376.55   $1,376.60