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 $59.44   13.786%   $67.6344   $67.63   $67.65   $67.60  
  Purchase #2 $248.97   7.633%   $267.9739   $267.97   $267.95   $268.00  
  Purchase #3 $239.55   3.287%   $247.424   $247.42   $247.40   $247.40  
  Purchase #4 $244.90   3.441%   $253.327   $253.33   $253.35   $253.30  
  Purchase #5 $96.92   12.299%   $108.8402   $108.84   $108.85   $108.80  
  Purchase #6 $152.43   7.617%   $164.0406   $164.04   $164.05   $164.00  
  Purchase #7 $243.46   13.655%   $276.7045   $276.70   $276.70   $276.70  
  7 purchase totals = $1,285.67       $1,385.9446   $1,385.93   $1,385.95   $1,385.80