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 $47.87   12.842%   $54.0175   $54.02   $54.00   $54.00  
  Purchase #2 $233.88   5.829%   $247.5129   $247.51   $247.50   $247.50  
  Purchase #3 $62.46   11.775%   $69.8147   $69.81   $69.80   $69.80  
  Purchase #4 $232.42   6.242%   $246.9277   $246.93   $246.95   $246.90  
  Purchase #5 $215.41   13.516%   $244.5248   $244.52   $244.50   $244.50  
  Purchase #6 $182.89   6.864%   $195.4436   $195.44   $195.45   $195.40  
  Purchase #7 $166.42   8.745%   $180.9734   $180.97   $180.95   $181.00  
  7 purchase totals = $1,141.35       $1,239.2146   $1,239.20   $1,239.15   $1,239.10