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 $175.38   13.616%   $199.2597   $199.26   $199.25   $199.30  
  Purchase #2 $11.54   11.138%   $12.8253   $12.83   $12.85   $12.80  
  Purchase #3 $195.69   3.209%   $201.9697   $201.97   $201.95   $202.00  
  Purchase #4 $53.81   7.216%   $57.6929   $57.69   $57.70   $57.70  
  Purchase #5 $245.84   11.582%   $274.3132   $274.31   $274.30   $274.30  
  Purchase #6 $32.47   11.581%   $36.2304   $36.23   $36.25   $36.20  
  Purchase #7 $88.95   7.799%   $95.8872   $95.89   $95.90   $95.90  
  7 purchase totals = $803.68       $878.1784   $878.18   $878.20   $878.20