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 $98.35   4.730%   $103.002   $103.00   $103.00   $103.00  
  Purchase #2 $48.92   10.603%   $54.107   $54.11   $54.10   $54.10  
  Purchase #3 $145.32   4.140%   $151.3362   $151.34   $151.35   $151.30  
  Purchase #4 $213.97   10.810%   $237.1002   $237.10   $237.10   $237.10  
  Purchase #5 $32.62   8.143%   $35.2762   $35.28   $35.30   $35.30  
  Purchase #6 $117.56   4.546%   $122.9043   $122.90   $122.90   $122.90  
  Purchase #7 $173.62   10.142%   $191.2285   $191.23   $191.25   $191.20  
  7 purchase totals = $830.36       $894.9544   $894.96   $895.00   $894.90