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 $217.92   8.127%   $235.6304   $235.63   $235.65   $235.60  
  Purchase #2 $41.93   12.533%   $47.1851   $47.19   $47.20   $47.20  
  Purchase #3 $185.74   3.109%   $191.5147   $191.51   $191.50   $191.50  
  Purchase #4 $180.79   9.732%   $198.3845   $198.38   $198.40   $198.40  
  Purchase #5 $212.43   6.617%   $226.4865   $226.49   $226.50   $226.50  
  Purchase #6 $45.38   10.196%   $50.0069   $50.01   $50.00   $50.00  
  Purchase #7 $119.97   11.647%   $133.9429   $133.94   $133.95   $133.90  
  7 purchase totals = $1,004.16       $1,083.1510   $1,083.15   $1,083.20   $1,083.10