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 $234.46   13.529%   $266.1801   $266.18   $266.20   $266.20  
  Purchase #2 $163.90   7.470%   $176.1433   $176.14   $176.15   $176.10  
  Purchase #3 $170.92   10.704%   $189.2153   $189.22   $189.20   $189.20  
  Purchase #4 $130.26   11.106%   $144.7267   $144.73   $144.75   $144.70  
  Purchase #5 $133.49   8.269%   $144.5283   $144.53   $144.55   $144.50  
  Purchase #6 $157.98   11.265%   $175.7764   $175.78   $175.80   $175.80  
  Purchase #7 $96.31   6.207%   $102.288   $102.29   $102.30   $102.30  
  7 purchase totals = $1,087.32       $1,198.8581   $1,198.87   $1,198.95   $1,198.80