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 $241.35   9.665%   $264.6765   $264.68   $264.70   $264.70  
  Purchase #2 $83.63   11.210%   $93.0049   $93.00   $93.00   $93.00  
  Purchase #3 $29.95   9.338%   $32.7467   $32.75   $32.75   $32.70  
  Purchase #4 $202.72   7.150%   $217.2145   $217.21   $217.20   $217.20  
  Purchase #5 $123.46   11.254%   $137.3542   $137.35   $137.35   $137.40  
  Purchase #6 $222.35   4.409%   $232.1534   $232.15   $232.15   $232.20  
  Purchase #7 $168.83   11.440%   $188.1442   $188.14   $188.15   $188.10  
  7 purchase totals = $1,072.29       $1,165.2944   $1,165.28   $1,165.30   $1,165.30