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 $48.93   8.609%   $53.1424   $53.14   $53.15   $53.10  
  Purchase #2 $248.44   4.714%   $260.1515   $260.15   $260.15   $260.20  
  Purchase #3 $40.79   3.679%   $42.2907   $42.29   $42.30   $42.30  
  Purchase #4 $112.93   5.871%   $119.5601   $119.56   $119.55   $119.60  
  Purchase #5 $149.35   3.674%   $154.8371   $154.84   $154.85   $154.80  
  Purchase #6 $19.55   5.705%   $20.6653   $20.67   $20.65   $20.70  
  Purchase #7 $106.69   12.812%   $120.3591   $120.36   $120.35   $120.40  
  7 purchase totals = $726.68       $771.0062   $771.01   $771.00   $771.10