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 $202.74   12.291%   $227.6588   $227.66   $227.65   $227.70  
  Purchase #2 $188.48   11.350%   $209.8725   $209.87   $209.85   $209.90  
  Purchase #3 $123.56   10.659%   $136.7303   $136.73   $136.75   $136.70  
  Purchase #4 $13.65   8.792%   $14.8501   $14.85   $14.85   $14.90  
  Purchase #5 $236.41   8.267%   $255.954   $255.95   $255.95   $256.00  
  Purchase #6 $129.52   8.654%   $140.7287   $140.73   $140.75   $140.70  
  Purchase #7 $56.44   9.524%   $61.8153   $61.82   $61.80   $61.80  
  7 purchase totals = $950.80       $1,047.6097   $1,047.61   $1,047.60   $1,047.70