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 $70.26   8.822%   $76.4583   $76.46   $76.45   $76.50  
  Purchase #2 $242.87   4.413%   $253.5879   $253.59   $253.60   $253.60  
  Purchase #3 $25.81   12.254%   $28.9728   $28.97   $28.95   $29.00  
  Purchase #4 $219.47   5.427%   $231.3806   $231.38   $231.40   $231.40  
  Purchase #5 $242.86   6.278%   $258.1068   $258.11   $258.10   $258.10  
  Purchase #6 $170.86   13.515%   $193.9517   $193.95   $193.95   $194.00  
  Purchase #7 $249.94   7.396%   $268.4256   $268.43   $268.45   $268.40  
  7 purchase totals = $1,222.07       $1,310.8837   $1,310.89   $1,310.90   $1,311.00