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 $233.77   11.638%   $260.9762   $260.98   $261.00   $261.00  
  Purchase #2 $187.51   11.410%   $208.9049   $208.90   $208.90   $208.90  
  Purchase #3 $240.32   13.286%   $272.2489   $272.25   $272.25   $272.20  
  Purchase #4 $138.63   10.525%   $153.2208   $153.22   $153.20   $153.20  
  Purchase #5 $41.92   9.829%   $46.0403   $46.04   $46.05   $46.00  
  Purchase #6 $165.50   6.784%   $176.7275   $176.73   $176.75   $176.70  
  Purchase #7 $32.71   4.547%   $34.1973   $34.20   $34.20   $34.20  
  7 purchase totals = $1,040.36       $1,152.3159   $1,152.32   $1,152.35   $1,152.20