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 $55.84   10.751%   $61.8434   $61.84   $61.85   $61.80  
  Purchase #2 $182.42   3.381%   $188.5876   $188.59   $188.60   $188.60  
  Purchase #3 $24.62   3.393%   $25.4554   $25.46   $25.45   $25.50  
  Purchase #4 $250.89   3.513%   $259.7038   $259.70   $259.70   $259.70  
  Purchase #5 $101.96   6.258%   $108.3407   $108.34   $108.35   $108.30  
  Purchase #6 $107.50   5.510%   $113.4233   $113.42   $113.40   $113.40  
  Purchase #7 $189.76   9.185%   $207.1895   $207.19   $207.20   $207.20  
  7 purchase totals = $912.99       $964.5437   $964.54   $964.55   $964.50