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 $228.40   6.579%   $243.4264   $243.43   $243.45   $243.40  
  Purchase #2 $55.90   6.106%   $59.3133   $59.31   $59.30   $59.30  
  Purchase #3 $180.77   6.386%   $192.314   $192.31   $192.30   $192.30  
  Purchase #4 $61.89   10.651%   $68.4819   $68.48   $68.50   $68.50  
  Purchase #5 $207.50   11.153%   $230.6425   $230.64   $230.65   $230.60  
  Purchase #6 $114.36   9.291%   $124.9852   $124.99   $125.00   $125.00  
  Purchase #7 $100.62   3.817%   $104.4607   $104.46   $104.45   $104.50  
  7 purchase totals = $949.44       $1,023.6240   $1,023.62   $1,023.65   $1,023.60