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 $55.91   3.568%   $57.9049   $57.90   $57.90   $57.90  
  Purchase #2 $75.95   13.692%   $86.3491   $86.35   $86.35   $86.30  
  Purchase #3 $206.77   5.451%   $218.041   $218.04   $218.05   $218.00  
  Purchase #4 $48.63   4.259%   $50.7012   $50.70   $50.70   $50.70  
  Purchase #5 $220.30   13.214%   $249.4104   $249.41   $249.40   $249.40  
  Purchase #6 $86.81   6.693%   $92.6202   $92.62   $92.60   $92.60  
  Purchase #7 $116.36   4.388%   $121.4659   $121.47   $121.45   $121.50  
  7 purchase totals = $810.73       $876.4927   $876.49   $876.45   $876.40