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 $87.42   5.721%   $92.4213   $92.42   $92.40   $92.40  
  Purchase #2 $83.72   9.756%   $91.8877   $91.89   $91.90   $91.90  
  Purchase #3 $107.26   11.658%   $119.7644   $119.76   $119.75   $119.80  
  Purchase #4 $40.90   11.719%   $45.6931   $45.69   $45.70   $45.70  
  Purchase #5 $204.42   10.248%   $225.369   $225.37   $225.35   $225.40  
  Purchase #6 $180.27   8.225%   $195.0972   $195.10   $195.10   $195.10  
  Purchase #7 $66.49   11.818%   $74.3478   $74.35   $74.35   $74.30  
  7 purchase totals = $770.48       $844.5805   $844.58   $844.55   $844.60