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 $78.34   7.574%   $84.2735   $84.27   $84.25   $84.30  
  Purchase #2 $212.79   6.381%   $226.3681   $226.37   $226.35   $226.40  
  Purchase #3 $88.88   4.777%   $93.1258   $93.13   $93.15   $93.10  
  Purchase #4 $127.79   4.201%   $133.1585   $133.16   $133.15   $133.20  
  Purchase #5 $220.44   7.696%   $237.4051   $237.41   $237.40   $237.40  
  Purchase #6 $206.28   3.263%   $213.0109   $213.01   $213.00   $213.00  
  Purchase #7 $34.36   3.500%   $35.5626   $35.56   $35.55   $35.60  
  7 purchase totals = $968.88       $1,022.9045   $1,022.91   $1,022.85   $1,023.00