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 $55.64   13.739%   $63.2844   $63.28   $63.30   $63.30  
  Purchase #2 $155.82   11.407%   $173.5944   $173.59   $173.60   $173.60  
  Purchase #3 $39.65   6.728%   $42.3177   $42.32   $42.30   $42.30  
  Purchase #4 $51.37   3.520%   $53.1782   $53.18   $53.20   $53.20  
  Purchase #5 $248.51   7.459%   $267.0464   $267.05   $267.05   $267.00  
  Purchase #6 $248.80   13.642%   $282.7413   $282.74   $282.75   $282.70  
  Purchase #7 $73.33   11.186%   $81.5327   $81.53   $81.55   $81.50  
  7 purchase totals = $873.12       $963.6951   $963.69   $963.75   $963.60