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 $61.32   10.250%   $67.6053   $67.61   $67.60   $67.60  
  Purchase #2 $211.35   13.204%   $239.2567   $239.26   $239.25   $239.30  
  Purchase #3 $22.80   8.643%   $24.7706   $24.77   $24.75   $24.80  
  Purchase #4 $204.99   11.410%   $228.3794   $228.38   $228.40   $228.40  
  Purchase #5 $188.99   3.587%   $195.7691   $195.77   $195.75   $195.80  
  Purchase #6 $75.48   9.281%   $82.4853   $82.49   $82.50   $82.50  
  Purchase #7 $69.72   3.515%   $72.1707   $72.17   $72.15   $72.20  
  7 purchase totals = $834.65       $910.4371   $910.45   $910.40   $910.60