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 $248.44   7.846%   $267.9326   $267.93   $267.95   $267.90  
  Purchase #2 $66.42   9.225%   $72.5472   $72.55   $72.55   $72.50  
  Purchase #3 $58.54   11.600%   $65.3306   $65.33   $65.35   $65.30  
  Purchase #4 $199.68   4.573%   $208.8114   $208.81   $208.80   $208.80  
  Purchase #5 $70.62   10.412%   $77.973   $77.97   $77.95   $78.00  
  Purchase #6 $78.61   5.277%   $82.7582   $82.76   $82.75   $82.80  
  Purchase #7 $62.79   9.819%   $68.9554   $68.96   $68.95   $69.00  
  7 purchase totals = $785.10       $844.3084   $844.31   $844.30   $844.30