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 $90.69   5.588%   $95.7578   $95.76   $95.75   $95.80  
  Purchase #2 $55.74   5.855%   $59.0036   $59.00   $59.00   $59.00  
  Purchase #3 $236.67   11.853%   $264.7225   $264.72   $264.70   $264.70  
  Purchase #4 $50.52   10.808%   $55.9802   $55.98   $56.00   $56.00  
  Purchase #5 $243.46   9.654%   $266.9636   $266.96   $266.95   $267.00  
  Purchase #6 $110.71   9.302%   $121.0082   $121.01   $121.00   $121.00  
  Purchase #7 $21.65   12.269%   $24.3062   $24.31   $24.30   $24.30  
  7 purchase totals = $809.44       $887.7421   $887.74   $887.70   $887.80