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 $132.96   5.356%   $140.0813   $140.08   $140.10   $140.10  
  Purchase #2 $40.91   13.445%   $46.4103   $46.41   $46.40   $46.40  
  Purchase #3 $189.65   8.276%   $205.3454   $205.35   $205.35   $205.30  
  Purchase #4 $203.83   3.507%   $210.9783   $210.98   $211.00   $211.00  
  Purchase #5 $155.29   4.848%   $162.8185   $162.82   $162.80   $162.80  
  Purchase #6 $28.31   12.207%   $31.7658   $31.77   $31.75   $31.80  
  Purchase #7 $136.32   4.547%   $142.5185   $142.52   $142.50   $142.50  
  7 purchase totals = $887.27       $939.9181   $939.93   $939.90   $939.90