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 $207.71   13.861%   $236.5007   $236.50   $236.50   $236.50  
  Purchase #2 $6.93   8.326%   $7.507   $7.51   $7.50   $7.50  
  Purchase #3 $26.45   9.152%   $28.8707   $28.87   $28.85   $28.90  
  Purchase #4 $68.62   12.779%   $77.3889   $77.39   $77.40   $77.40  
  Purchase #5 $207.88   5.708%   $219.7458   $219.75   $219.75   $219.70  
  Purchase #6 $124.99   7.830%   $134.7767   $134.78   $134.80   $134.80  
  Purchase #7 $109.27   10.826%   $121.0996   $121.10   $121.10   $121.10  
  7 purchase totals = $751.85       $825.8894   $825.90   $825.90   $825.90