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 $83.86   9.659%   $91.96   $91.96   $91.95   $92.00  
  Purchase #2 $120.90   5.670%   $127.755   $127.76   $127.75   $127.80  
  Purchase #3 $222.76   12.555%   $250.7275   $250.73   $250.75   $250.70  
  Purchase #4 $91.86   3.611%   $95.1771   $95.18   $95.20   $95.20  
  Purchase #5 $139.34   6.632%   $148.581   $148.58   $148.60   $148.60  
  Purchase #6 $213.49   5.108%   $224.3951   $224.40   $224.40   $224.40  
  Purchase #7 $123.25   5.433%   $129.9462   $129.95   $129.95   $129.90  
  7 purchase totals = $995.46       $1,068.5419   $1,068.56   $1,068.60   $1,068.60