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 $61.54   10.502%   $68.0029   $68.00   $68.00   $68.00  
  Purchase #2 $48.29   5.326%   $50.8619   $50.86   $50.85   $50.90  
  Purchase #3 $213.61   11.115%   $237.3528   $237.35   $237.35   $237.40  
  Purchase #4 $48.36   9.480%   $52.9445   $52.94   $52.95   $52.90  
  Purchase #5 $67.40   11.220%   $74.9623   $74.96   $74.95   $75.00  
  Purchase #6 $180.42   8.845%   $196.3781   $196.38   $196.40   $196.40  
  Purchase #7 $243.42   5.749%   $257.4142   $257.41   $257.40   $257.40  
  7 purchase totals = $863.04       $937.9167   $937.90   $937.90   $938.00