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 $58.90   11.516%   $65.6829   $65.68   $65.70   $65.70  
  Purchase #2 $232.86   5.475%   $245.6091   $245.61   $245.60   $245.60  
  Purchase #3 $202.28   6.615%   $215.6608   $215.66   $215.65   $215.70  
  Purchase #4 $129.30   5.362%   $136.2331   $136.23   $136.25   $136.20  
  Purchase #5 $28.70   11.331%   $31.952   $31.95   $31.95   $32.00  
  Purchase #6 $146.45   10.432%   $161.7277   $161.73   $161.75   $161.70  
  Purchase #7 $53.73   6.712%   $57.3364   $57.34   $57.35   $57.30  
  7 purchase totals = $852.22       $914.2020   $914.20   $914.25   $914.20