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 $110.44   13.655%   $125.5206   $125.52   $125.50   $125.50  
  Purchase #2 $214.55   8.562%   $232.9198   $232.92   $232.90   $232.90  
  Purchase #3 $118.29   4.265%   $123.3351   $123.34   $123.35   $123.30  
  Purchase #4 $238.36   11.701%   $266.2505   $266.25   $266.25   $266.30  
  Purchase #5 $184.61   8.678%   $200.6305   $200.63   $200.65   $200.60  
  Purchase #6 $159.82   8.574%   $173.523   $173.52   $173.50   $173.50  
  Purchase #7 $104.79   13.422%   $118.8549   $118.85   $118.85   $118.90  
  7 purchase totals = $1,130.86       $1,241.0344   $1,241.03   $1,241.00   $1,241.00