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 $232.93   11.317%   $259.2907   $259.29   $259.30   $259.30  
  Purchase #2 $10.83   12.453%   $12.1787   $12.18   $12.20   $12.20  
  Purchase #3 $210.44   11.831%   $235.3372   $235.34   $235.35   $235.30  
  Purchase #4 $24.36   13.124%   $27.557   $27.56   $27.55   $27.60  
  Purchase #5 $227.74   6.517%   $242.5818   $242.58   $242.60   $242.60  
  Purchase #6 $58.75   5.227%   $61.8209   $61.82   $61.80   $61.80  
  Purchase #7 $55.40   12.837%   $62.5117   $62.51   $62.50   $62.50  
  7 purchase totals = $820.45       $901.2780   $901.28   $901.30   $901.30