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 $84.35   11.200%   $93.7972   $93.80   $93.80   $93.80  
  Purchase #2 $34.91   6.633%   $37.2256   $37.23   $37.25   $37.20  
  Purchase #3 $150.57   4.782%   $157.7703   $157.77   $157.75   $157.80  
  Purchase #4 $148.73   9.531%   $162.9055   $162.91   $162.90   $162.90  
  Purchase #5 $120.43   3.129%   $124.1983   $124.20   $124.20   $124.20  
  Purchase #6 $190.60   8.551%   $206.8982   $206.90   $206.90   $206.90  
  Purchase #7 $226.33   12.176%   $253.8879   $253.89   $253.90   $253.90  
  7 purchase totals = $955.92       $1,036.6830   $1,036.70   $1,036.70   $1,036.70