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 $184.71   13.620%   $209.8675   $209.87   $209.85   $209.90  
  Purchase #2 $206.96   10.137%   $227.9395   $227.94   $227.95   $227.90  
  Purchase #3 $221.39   11.669%   $247.224   $247.22   $247.20   $247.20  
  Purchase #4 $134.60   6.464%   $143.3005   $143.30   $143.30   $143.30  
  Purchase #5 $190.37   5.639%   $201.105   $201.11   $201.10   $201.10  
  Purchase #6 $86.72   5.779%   $91.7315   $91.73   $91.75   $91.70  
  Purchase #7 $236.92   10.183%   $261.0456   $261.05   $261.05   $261.00  
  7 purchase totals = $1,261.67       $1,382.2136   $1,382.22   $1,382.20   $1,382.10