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 $46.61   8.429%   $50.5388   $50.54   $50.55   $50.50  
  Purchase #2 $233.78   11.468%   $260.5899   $260.59   $260.60   $260.60  
  Purchase #3 $143.32   13.735%   $163.005   $163.01   $163.00   $163.00  
  Purchase #4 $59.83   11.827%   $66.9061   $66.91   $66.90   $66.90  
  Purchase #5 $142.69   3.754%   $148.0466   $148.05   $148.05   $148.00  
  Purchase #6 $193.73   10.767%   $214.5889   $214.59   $214.60   $214.60  
  Purchase #7 $214.27   7.574%   $230.4988   $230.50   $230.50   $230.50  
  7 purchase totals = $1,034.23       $1,134.1741   $1,134.19   $1,134.20   $1,134.10