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 $43.26   13.602%   $49.1442   $49.14   $49.15   $49.10  
  Purchase #2 $211.51   13.725%   $240.5397   $240.54   $240.55   $240.50  
  Purchase #3 $67.56   4.543%   $70.6293   $70.63   $70.65   $70.60  
  Purchase #4 $185.42   5.202%   $195.0655   $195.07   $195.05   $195.10  
  Purchase #5 $174.36   9.362%   $190.6836   $190.68   $190.70   $190.70  
  Purchase #6 $190.72   11.682%   $212.9999   $213.00   $213.00   $213.00  
  Purchase #7 $178.96   5.690%   $189.1428   $189.14   $189.15   $189.10  
  7 purchase totals = $1,051.79       $1,148.2050   $1,148.20   $1,148.25   $1,148.10