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 $92.52   13.792%   $105.2804   $105.28   $105.30   $105.30  
  Purchase #2 $119.44   11.412%   $133.0705   $133.07   $133.05   $133.10  
  Purchase #3 $199.98   13.457%   $226.8913   $226.89   $226.90   $226.90  
  Purchase #4 $111.73   11.602%   $124.6929   $124.69   $124.70   $124.70  
  Purchase #5 $233.58   13.622%   $265.3983   $265.40   $265.40   $265.40  
  Purchase #6 $43.56   5.145%   $45.8012   $45.80   $45.80   $45.80  
  Purchase #7 $243.38   6.802%   $259.9347   $259.93   $259.95   $259.90  
  7 purchase totals = $1,044.19       $1,161.0693   $1,161.06   $1,161.10   $1,161.10