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 $181.87   6.386%   $193.4842   $193.48   $193.50   $193.50  
  Purchase #2 $157.99   6.629%   $168.4632   $168.46   $168.45   $168.50  
  Purchase #3 $106.29   12.625%   $119.7091   $119.71   $119.70   $119.70  
  Purchase #4 $11.75   13.590%   $13.3468   $13.35   $13.35   $13.30  
  Purchase #5 $55.95   8.765%   $60.854   $60.85   $60.85   $60.90  
  Purchase #6 $228.45   10.861%   $253.262   $253.26   $253.25   $253.30  
  Purchase #7 $89.49   9.712%   $98.1813   $98.18   $98.20   $98.20  
  7 purchase totals = $831.79       $907.3006   $907.29   $907.30   $907.40