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 $29.62   8.371%   $32.0995   $32.10   $32.10   $32.10  
  Purchase #2 $123.26   10.462%   $136.1555   $136.16   $136.15   $136.20  
  Purchase #3 $240.66   10.811%   $266.6778   $266.68   $266.70   $266.70  
  Purchase #4 $204.75   9.380%   $223.9556   $223.96   $223.95   $224.00  
  Purchase #5 $65.62   10.159%   $72.2863   $72.29   $72.30   $72.30  
  Purchase #6 $67.44   13.402%   $76.4783   $76.48   $76.50   $76.50  
  Purchase #7 $176.39   9.833%   $193.7344   $193.73   $193.75   $193.70  
  7 purchase totals = $907.74       $1,001.3874   $1,001.40   $1,001.45   $1,001.50