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 $236.29   3.193%   $243.8347   $243.83   $243.85   $243.80  
  Purchase #2 $153.52   4.454%   $160.3578   $160.36   $160.35   $160.40  
  Purchase #3 $90.99   6.550%   $96.9498   $96.95   $96.95   $96.90  
  Purchase #4 $26.87   3.824%   $27.8975   $27.90   $27.90   $27.90  
  Purchase #5 $163.38   11.584%   $182.3059   $182.31   $182.30   $182.30  
  Purchase #6 $217.72   4.520%   $227.5609   $227.56   $227.55   $227.60  
  Purchase #7 $25.65   13.477%   $29.1069   $29.11   $29.10   $29.10  
  7 purchase totals = $914.42       $968.0135   $968.02   $968.00   $968.00