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 $192.94   6.416%   $205.319   $205.32   $205.30   $205.30  
  Purchase #2 $84.65   8.286%   $91.6641   $91.66   $91.65   $91.70  
  Purchase #3 $239.28   8.226%   $258.9632   $258.96   $258.95   $259.00  
  Purchase #4 $64.36   11.518%   $71.773   $71.77   $71.75   $71.80  
  Purchase #5 $32.73   12.386%   $36.7839   $36.78   $36.80   $36.80  
  Purchase #6 $94.31   4.480%   $98.5351   $98.54   $98.55   $98.50  
  Purchase #7 $132.95   8.856%   $144.7241   $144.72   $144.70   $144.70  
  7 purchase totals = $841.22       $907.7624   $907.75   $907.70   $907.80