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 $49.33   5.402%   $51.9948   $51.99   $52.00   $52.00  
  Purchase #2 $177.47   13.784%   $201.9325   $201.93   $201.95   $201.90  
  Purchase #3 $68.50   7.496%   $73.6348   $73.63   $73.65   $73.60  
  Purchase #4 $164.35   9.838%   $180.5188   $180.52   $180.50   $180.50  
  Purchase #5 $249.81   12.397%   $280.7789   $280.78   $280.80   $280.80  
  Purchase #6 $111.73   8.534%   $121.265   $121.27   $121.25   $121.30  
  Purchase #7 $41.69   12.300%   $46.8179   $46.82   $46.80   $46.80  
  7 purchase totals = $862.88       $956.9427   $956.94   $956.95   $956.90