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 $168.47   4.722%   $176.4252   $176.43   $176.45   $176.40  
  Purchase #2 $55.93   4.467%   $58.4284   $58.43   $58.45   $58.40  
  Purchase #3 $54.81   8.571%   $59.5078   $59.51   $59.50   $59.50  
  Purchase #4 $219.32   11.330%   $244.169   $244.17   $244.15   $244.20  
  Purchase #5 $76.98   12.576%   $86.661   $86.66   $86.65   $86.70  
  Purchase #6 $197.93   11.433%   $220.5593   $220.56   $220.55   $220.60  
  Purchase #7 $117.35   10.676%   $129.8783   $129.88   $129.90   $129.90  
  7 purchase totals = $890.79       $975.6290   $975.64   $975.65   $975.70