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 $211.42   8.781%   $229.9848   $229.98   $230.00   $230.00  
  Purchase #2 $239.94   11.265%   $266.9692   $266.97   $266.95   $267.00  
  Purchase #3 $171.42   5.105%   $180.171   $180.17   $180.15   $180.20  
  Purchase #4 $104.46   12.846%   $117.8789   $117.88   $117.90   $117.90  
  Purchase #5 $20.88   12.841%   $23.5612   $23.56   $23.55   $23.60  
  Purchase #6 $238.52   3.369%   $246.5557   $246.56   $246.55   $246.60  
  Purchase #7 $5.72   3.186%   $5.9022   $5.90   $5.90   $5.90  
  7 purchase totals = $992.36       $1,071.0230   $1,071.02   $1,071.00   $1,071.20