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 $52.55   9.703%   $57.6489   $57.65   $57.65   $57.60  
  Purchase #2 $220.35   10.835%   $244.2249   $244.22   $244.20   $244.20  
  Purchase #3 $173.94   8.711%   $189.0919   $189.09   $189.10   $189.10  
  Purchase #4 $9.92   5.482%   $10.4638   $10.46   $10.45   $10.50  
  Purchase #5 $70.27   7.603%   $75.6126   $75.61   $75.60   $75.60  
  Purchase #6 $125.34   5.672%   $132.4493   $132.45   $132.45   $132.40  
  Purchase #7 $67.97   8.844%   $73.9813   $73.98   $74.00   $74.00  
  7 purchase totals = $720.34       $783.4727   $783.46   $783.45   $783.40