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 $217.43   8.518%   $235.9507   $235.95   $235.95   $236.00  
  Purchase #2 $59.92   9.148%   $65.4015   $65.40   $65.40   $65.40  
  Purchase #3 $176.42   3.524%   $182.637   $182.64   $182.65   $182.60  
  Purchase #4 $198.27   13.614%   $225.2625   $225.26   $225.25   $225.30  
  Purchase #5 $22.46   5.648%   $23.7285   $23.73   $23.75   $23.70  
  Purchase #6 $212.90   10.579%   $235.4227   $235.42   $235.40   $235.40  
  Purchase #7 $71.43   12.487%   $80.3495   $80.35   $80.35   $80.30  
  7 purchase totals = $958.83       $1,048.7524   $1,048.75   $1,048.75   $1,048.70