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 $66.93   3.171%   $69.0524   $69.05   $69.05   $69.10  
  Purchase #2 $250.81   9.231%   $273.9623   $273.96   $273.95   $274.00  
  Purchase #3 $110.86   8.857%   $120.6789   $120.68   $120.70   $120.70  
  Purchase #4 $88.90   8.322%   $96.2983   $96.30   $96.30   $96.30  
  Purchase #5 $143.72   6.719%   $153.3765   $153.38   $153.40   $153.40  
  Purchase #6 $6.77   7.209%   $7.258   $7.26   $7.25   $7.30  
  Purchase #7 $170.84   13.597%   $194.0691   $194.07   $194.05   $194.10  
  7 purchase totals = $838.83       $914.6955   $914.70   $914.70   $914.90