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 $44.42   11.611%   $49.5776   $49.58   $49.60   $49.60  
  Purchase #2 $231.86   6.381%   $246.655   $246.66   $246.65   $246.70  
  Purchase #3 $175.75   4.453%   $183.5761   $183.58   $183.60   $183.60  
  Purchase #4 $94.83   9.807%   $104.13   $104.13   $104.15   $104.10  
  Purchase #5 $84.86   9.556%   $92.9692   $92.97   $92.95   $93.00  
  Purchase #6 $147.73   6.344%   $157.102   $157.10   $157.10   $157.10  
  Purchase #7 $20.26   10.680%   $22.4238   $22.42   $22.40   $22.40  
  7 purchase totals = $799.71       $856.4337   $856.44   $856.45   $856.50