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 $250.90   6.716%   $267.7504   $267.75   $267.75   $267.80  
  Purchase #2 $117.99   11.674%   $131.7642   $131.76   $131.75   $131.80  
  Purchase #3 $226.86   7.170%   $243.1259   $243.13   $243.15   $243.10  
  Purchase #4 $50.75   4.604%   $53.0865   $53.09   $53.10   $53.10  
  Purchase #5 $42.62   4.397%   $44.494   $44.49   $44.50   $44.50  
  Purchase #6 $156.93   9.211%   $171.3848   $171.38   $171.40   $171.40  
  Purchase #7 $124.98   13.478%   $141.8248   $141.82   $141.80   $141.80  
  7 purchase totals = $971.03       $1,053.4306   $1,053.42   $1,053.45   $1,053.50