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 $105.77   13.363%   $119.904   $119.90   $119.90   $119.90  
  Purchase #2 $50.91   6.636%   $54.2884   $54.29   $54.30   $54.30  
  Purchase #3 $167.90   7.475%   $180.4505   $180.45   $180.45   $180.50  
  Purchase #4 $107.27   11.396%   $119.4945   $119.49   $119.50   $119.50  
  Purchase #5 $158.63   11.136%   $176.295   $176.30   $176.30   $176.30  
  Purchase #6 $223.33   4.205%   $232.721   $232.72   $232.70   $232.70  
  Purchase #7 $143.94   12.302%   $161.6475   $161.65   $161.65   $161.60  
  7 purchase totals = $957.75       $1,044.8009   $1,044.80   $1,044.80   $1,044.80