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 $84.71   4.569%   $88.5804   $88.58   $88.60   $88.60  
  Purchase #2 $101.63   9.507%   $111.292   $111.29   $111.30   $111.30  
  Purchase #3 $22.40   12.211%   $25.1353   $25.14   $25.15   $25.10  
  Purchase #4 $212.29   11.663%   $237.0494   $237.05   $237.05   $237.00  
  Purchase #5 $71.95   4.721%   $75.3468   $75.35   $75.35   $75.30  
  Purchase #6 $241.47   10.412%   $266.6119   $266.61   $266.60   $266.60  
  Purchase #7 $191.91   8.728%   $208.6599   $208.66   $208.65   $208.70  
  7 purchase totals = $926.36       $1,012.6757   $1,012.68   $1,012.70   $1,012.60