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 $76.76   10.665%   $84.9465   $84.95   $84.95   $84.90  
  Purchase #2 $203.73   3.381%   $210.6181   $210.62   $210.60   $210.60  
  Purchase #3 $29.37   6.331%   $31.2294   $31.23   $31.25   $31.20  
  Purchase #4 $191.40   7.289%   $205.3511   $205.35   $205.35   $205.40  
  Purchase #5 $128.34   12.281%   $144.1014   $144.10   $144.10   $144.10  
  Purchase #6 $13.35   8.185%   $14.4427   $14.44   $14.45   $14.40  
  Purchase #7 $168.85   7.316%   $181.2031   $181.20   $181.20   $181.20  
  7 purchase totals = $811.80       $871.8923   $871.89   $871.90   $871.80