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 $45.86   7.401%   $49.2541   $49.25   $49.25   $49.30  
  Purchase #2 $65.94   5.527%   $69.5845   $69.58   $69.60   $69.60  
  Purchase #3 $126.26   6.500%   $134.4669   $134.47   $134.45   $134.50  
  Purchase #4 $208.48   4.148%   $217.1278   $217.13   $217.15   $217.10  
  Purchase #5 $194.98   10.196%   $214.8602   $214.86   $214.85   $214.90  
  Purchase #6 $230.92   5.770%   $244.2441   $244.24   $244.25   $244.20  
  Purchase #7 $91.86   3.237%   $94.8335   $94.83   $94.85   $94.80  
  7 purchase totals = $964.30       $1,024.3711   $1,024.36   $1,024.40   $1,024.40