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 $136.47   12.811%   $153.9532   $153.95   $153.95   $154.00  
  Purchase #2 $92.25   8.228%   $99.8403   $99.84   $99.85   $99.80  
  Purchase #3 $42.80   7.367%   $45.9531   $45.95   $45.95   $46.00  
  Purchase #4 $70.75   7.867%   $76.3159   $76.32   $76.30   $76.30  
  Purchase #5 $70.99   5.198%   $74.6801   $74.68   $74.70   $74.70  
  Purchase #6 $222.98   13.356%   $252.7612   $252.76   $252.75   $252.80  
  Purchase #7 $183.65   11.736%   $205.2032   $205.20   $205.20   $205.20  
  7 purchase totals = $819.89       $908.7070   $908.70   $908.70   $908.80