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 $204.85   10.817%   $227.0086   $227.01   $227.00   $227.00  
  Purchase #2 $62.64   5.311%   $65.9668   $65.97   $65.95   $66.00  
  Purchase #3 $171.97   4.259%   $179.2942   $179.29   $179.30   $179.30  
  Purchase #4 $179.42   5.737%   $189.7133   $189.71   $189.70   $189.70  
  Purchase #5 $245.90   7.656%   $264.7261   $264.73   $264.75   $264.70  
  Purchase #6 $207.48   10.202%   $228.6471   $228.65   $228.65   $228.60  
  Purchase #7 $128.38   8.517%   $139.3141   $139.31   $139.30   $139.30  
  7 purchase totals = $1,200.64       $1,294.6702   $1,294.67   $1,294.65   $1,294.60