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 $224.62   7.286%   $240.9858   $240.99   $241.00   $241.00  
  Purchase #2 $48.25   10.267%   $53.2038   $53.20   $53.20   $53.20  
  Purchase #3 $138.31   7.219%   $148.2946   $148.29   $148.30   $148.30  
  Purchase #4 $59.65   8.439%   $64.6839   $64.68   $64.70   $64.70  
  Purchase #5 $79.55   13.332%   $90.1556   $90.16   $90.15   $90.20  
  Purchase #6 $83.54   10.573%   $92.3727   $92.37   $92.35   $92.40  
  Purchase #7 $58.67   5.861%   $62.1086   $62.11   $62.10   $62.10  
  7 purchase totals = $692.59       $751.8050   $751.80   $751.80   $751.90