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 $55.51   6.532%   $59.1359   $59.14   $59.15   $59.10  
  Purchase #2 $171.27   13.864%   $195.0149   $195.01   $195.00   $195.00  
  Purchase #3 $134.97   8.214%   $146.0564   $146.06   $146.05   $146.10  
  Purchase #4 $181.78   13.432%   $206.1967   $206.20   $206.20   $206.20  
  Purchase #5 $14.61   7.632%   $15.725   $15.73   $15.75   $15.70  
  Purchase #6 $197.26   6.350%   $209.786   $209.79   $209.80   $209.80  
  Purchase #7 $105.69   7.696%   $113.8239   $113.82   $113.80   $113.80  
  7 purchase totals = $861.09       $945.7388   $945.75   $945.75   $945.70