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 $54.47   13.109%   $61.6105   $61.61   $61.60   $61.60  
  Purchase #2 $199.80   7.797%   $215.3784   $215.38   $215.40   $215.40  
  Purchase #3 $20.86   9.510%   $22.8438   $22.84   $22.85   $22.80  
  Purchase #4 $107.72   11.353%   $119.9495   $119.95   $119.95   $119.90  
  Purchase #5 $225.58   4.187%   $235.025   $235.03   $235.05   $235.00  
  Purchase #6 $40.97   10.593%   $45.31   $45.31   $45.30   $45.30  
  Purchase #7 $57.35   10.350%   $63.2857   $63.29   $63.30   $63.30  
  7 purchase totals = $706.75       $763.4029   $763.41   $763.45   $763.30