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 $52.97   3.561%   $54.8563   $54.86   $54.85   $54.90  
  Purchase #2 $125.65   6.145%   $133.3712   $133.37   $133.35   $133.40  
  Purchase #3 $168.88   4.744%   $176.8917   $176.89   $176.90   $176.90  
  Purchase #4 $241.66   4.679%   $252.9673   $252.97   $252.95   $253.00  
  Purchase #5 $171.91   12.521%   $193.4349   $193.43   $193.45   $193.40  
  Purchase #6 $65.59   5.864%   $69.4362   $69.44   $69.45   $69.40  
  Purchase #7 $73.89   7.366%   $79.3327   $79.33   $79.35   $79.30  
  7 purchase totals = $900.55       $960.2903   $960.29   $960.30   $960.30