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 $41.87   13.753%   $47.6284   $47.63   $47.65   $47.60  
  Purchase #2 $109.55   8.111%   $118.4356   $118.44   $118.45   $118.40  
  Purchase #3 $233.40   6.130%   $247.7074   $247.71   $247.70   $247.70  
  Purchase #4 $148.65   10.337%   $164.016   $164.02   $164.00   $164.00  
  Purchase #5 $249.92   13.156%   $282.7995   $282.80   $282.80   $282.80  
  Purchase #6 $36.68   9.869%   $40.2999   $40.30   $40.30   $40.30  
  Purchase #7 $90.32   3.319%   $93.3177   $93.32   $93.30   $93.30  
  7 purchase totals = $910.39       $994.2045   $994.22   $994.20   $994.10