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 $119.53   12.719%   $134.733   $134.73   $134.75   $134.70  
  Purchase #2 $151.63   13.283%   $171.771   $171.77   $171.75   $171.80  
  Purchase #3 $119.98   5.403%   $126.4625   $126.46   $126.45   $126.50  
  Purchase #4 $63.42   5.638%   $66.9956   $67.00   $67.00   $67.00  
  Purchase #5 $85.86   11.449%   $95.6901   $95.69   $95.70   $95.70  
  Purchase #6 $125.40   7.243%   $134.4827   $134.48   $134.50   $134.50  
  Purchase #7 $181.65   12.473%   $204.3072   $204.31   $204.30   $204.30  
  7 purchase totals = $847.47       $934.4421   $934.44   $934.45   $934.50