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 $54.45   9.422%   $59.5803   $59.58   $59.60   $59.60  
  Purchase #2 $221.79   10.261%   $244.5479   $244.55   $244.55   $244.50  
  Purchase #3 $70.87   9.573%   $77.6544   $77.65   $77.65   $77.70  
  Purchase #4 $8.85   7.415%   $9.5062   $9.51   $9.50   $9.50  
  Purchase #5 $16.94   13.369%   $19.2047   $19.20   $19.20   $19.20  
  Purchase #6 $238.33   4.727%   $249.5959   $249.60   $249.60   $249.60  
  Purchase #7 $229.84   5.733%   $243.0167   $243.02   $243.00   $243.00  
  7 purchase totals = $841.07       $903.1061   $903.11   $903.10   $903.10