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 $45.55   4.328%   $47.5214   $47.52   $47.50   $47.50  
  Purchase #2 $224.37   13.255%   $254.1102   $254.11   $254.10   $254.10  
  Purchase #3 $194.73   11.700%   $217.5134   $217.51   $217.50   $217.50  
  Purchase #4 $78.44   11.511%   $87.4692   $87.47   $87.45   $87.50  
  Purchase #5 $125.54   3.779%   $130.2842   $130.28   $130.30   $130.30  
  Purchase #6 $48.28   8.608%   $52.4359   $52.44   $52.45   $52.40  
  Purchase #7 $227.84   6.867%   $243.4858   $243.49   $243.50   $243.50  
  7 purchase totals = $944.75       $1,032.8201   $1,032.82   $1,032.80   $1,032.80