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 $50.50   6.458%   $53.7613   $53.76   $53.75   $53.80  
  Purchase #2 $246.89   4.181%   $257.2125   $257.21   $257.20   $257.20  
  Purchase #3 $248.44   9.722%   $272.5933   $272.59   $272.60   $272.60  
  Purchase #4 $62.45   7.661%   $67.2343   $67.23   $67.25   $67.20  
  Purchase #5 $222.40   6.178%   $236.1399   $236.14   $236.15   $236.10  
  Purchase #6 $232.65   5.290%   $244.9572   $244.96   $244.95   $245.00  
  Purchase #7 $208.27   5.563%   $219.8561   $219.86   $219.85   $219.90  
  7 purchase totals = $1,271.60       $1,351.7546   $1,351.75   $1,351.75   $1,351.80