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 $215.53   11.834%   $241.0358   $241.04   $241.05   $241.00  
  Purchase #2 $205.55   5.772%   $217.4143   $217.41   $217.40   $217.40  
  Purchase #3 $52.82   8.515%   $57.3176   $57.32   $57.30   $57.30  
  Purchase #4 $44.63   6.389%   $47.4814   $47.48   $47.50   $47.50  
  Purchase #5 $240.62   4.300%   $250.9667   $250.97   $250.95   $251.00  
  Purchase #6 $194.61   8.423%   $211.002   $211.00   $211.00   $211.00  
  Purchase #7 $227.92   4.554%   $238.2995   $238.30   $238.30   $238.30  
  7 purchase totals = $1,181.68       $1,263.5173   $1,263.52   $1,263.50   $1,263.50