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 $32.71   10.721%   $36.2168   $36.22   $36.20   $36.20  
  Purchase #2 $196.85   9.455%   $215.4622   $215.46   $215.45   $215.50  
  Purchase #3 $125.56   12.271%   $140.9675   $140.97   $140.95   $141.00  
  Purchase #4 $169.90   3.466%   $175.7887   $175.79   $175.80   $175.80  
  Purchase #5 $26.80   5.701%   $28.3279   $28.33   $28.35   $28.30  
  Purchase #6 $108.33   7.154%   $116.0799   $116.08   $116.10   $116.10  
  Purchase #7 $222.59   4.672%   $232.9894   $232.99   $233.00   $233.00  
  7 purchase totals = $882.74       $945.8324   $945.84   $945.85   $945.90