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 $42.58   8.115%   $46.0354   $46.04   $46.05   $46.00  
  Purchase #2 $20.26   10.453%   $22.3778   $22.38   $22.40   $22.40  
  Purchase #3 $145.76   10.160%   $160.5692   $160.57   $160.55   $160.60  
  Purchase #4 $226.78   7.106%   $242.895   $242.90   $242.90   $242.90  
  Purchase #5 $90.38   11.762%   $101.0105   $101.01   $101.00   $101.00  
  Purchase #6 $92.86   10.826%   $102.913   $102.91   $102.90   $102.90  
  Purchase #7 $180.78   8.348%   $195.8715   $195.87   $195.85   $195.90  
  7 purchase totals = $799.40       $871.6724   $871.68   $871.65   $871.70