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 $206.33   11.605%   $230.2746   $230.27   $230.25   $230.30  
  Purchase #2 $113.98   4.619%   $119.2447   $119.24   $119.25   $119.20  
  Purchase #3 $158.94   5.655%   $167.9281   $167.93   $167.95   $167.90  
  Purchase #4 $36.69   13.335%   $41.5826   $41.58   $41.60   $41.60  
  Purchase #5 $15.84   4.631%   $16.5736   $16.57   $16.55   $16.60  
  Purchase #6 $159.50   5.358%   $168.046   $168.05   $168.05   $168.00  
  Purchase #7 $80.60   8.867%   $87.7468   $87.75   $87.75   $87.70  
  7 purchase totals = $771.88       $831.3964   $831.39   $831.40   $831.30