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 $180.61   7.220%   $193.65   $193.65   $193.65   $193.70  
  Purchase #2 $62.94   9.659%   $69.0194   $69.02   $69.00   $69.00  
  Purchase #3 $85.73   7.591%   $92.2378   $92.24   $92.25   $92.20  
  Purchase #4 $49.26   13.250%   $55.787   $55.79   $55.80   $55.80  
  Purchase #5 $47.89   5.377%   $50.465   $50.47   $50.45   $50.50  
  Purchase #6 $240.57   6.314%   $255.7596   $255.76   $255.75   $255.80  
  Purchase #7 $188.68   10.108%   $207.7518   $207.75   $207.75   $207.80  
  7 purchase totals = $855.68       $924.6706   $924.68   $924.65   $924.80