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 $237.43   7.396%   $254.9903   $254.99   $255.00   $255.00  
  Purchase #2 $163.71   7.453%   $175.9113   $175.91   $175.90   $175.90  
  Purchase #3 $52.97   11.315%   $58.9636   $58.96   $58.95   $59.00  
  Purchase #4 $220.66   7.137%   $236.4085   $236.41   $236.40   $236.40  
  Purchase #5 $147.84   3.233%   $152.6197   $152.62   $152.60   $152.60  
  Purchase #6 $31.59   10.793%   $34.9995   $35.00   $35.00   $35.00  
  Purchase #7 $98.68   4.515%   $103.1354   $103.14   $103.15   $103.10  
  7 purchase totals = $952.88       $1,017.0283   $1,017.03   $1,017.00   $1,017.00