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 $204.95   11.705%   $228.9394   $228.94   $228.95   $228.90  
  Purchase #2 $76.59   10.581%   $84.694   $84.69   $84.70   $84.70  
  Purchase #3 $219.94   10.266%   $242.519   $242.52   $242.50   $242.50  
  Purchase #4 $73.57   6.443%   $78.3101   $78.31   $78.30   $78.30  
  Purchase #5 $152.36   3.655%   $157.9288   $157.93   $157.95   $157.90  
  Purchase #6 $61.84   8.315%   $66.982   $66.98   $67.00   $67.00  
  Purchase #7 $30.98   13.814%   $35.2596   $35.26   $35.25   $35.30  
  7 purchase totals = $820.23       $894.6329   $894.63   $894.65   $894.60