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 $219.96   7.484%   $236.4218   $236.42   $236.40   $236.40  
  Purchase #2 $134.71   6.772%   $143.8326   $143.83   $143.85   $143.80  
  Purchase #3 $75.47   8.694%   $82.0314   $82.03   $82.05   $82.00  
  Purchase #4 $70.36   10.124%   $77.4832   $77.48   $77.50   $77.50  
  Purchase #5 $163.48   7.779%   $176.1971   $176.20   $176.20   $176.20  
  Purchase #6 $166.39   11.621%   $185.7262   $185.73   $185.75   $185.70  
  Purchase #7 $104.82   13.391%   $118.8564   $118.86   $118.85   $118.90  
  7 purchase totals = $935.19       $1,020.5487   $1,020.55   $1,020.60   $1,020.50