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 $88.27   5.336%   $92.9801   $92.98   $93.00   $93.00  
  Purchase #2 $228.96   3.310%   $236.5386   $236.54   $236.55   $236.50  
  Purchase #3 $145.98   10.709%   $161.613   $161.61   $161.60   $161.60  
  Purchase #4 $134.88   10.547%   $149.1058   $149.11   $149.10   $149.10  
  Purchase #5 $162.38   6.765%   $173.365   $173.37   $173.35   $173.40  
  Purchase #6 $26.44   9.477%   $28.9457   $28.95   $28.95   $28.90  
  Purchase #7 $94.62   9.380%   $103.4954   $103.50   $103.50   $103.50  
  7 purchase totals = $881.53       $946.0436   $946.06   $946.05   $946.00