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 $62.61   13.684%   $71.1776   $71.18   $71.20   $71.20  
  Purchase #2 $238.28   11.460%   $265.5869   $265.59   $265.60   $265.60  
  Purchase #3 $138.65   9.465%   $151.7732   $151.77   $151.75   $151.80  
  Purchase #4 $116.70   5.386%   $122.9855   $122.99   $123.00   $123.00  
  Purchase #5 $124.56   4.510%   $130.1777   $130.18   $130.20   $130.20  
  Purchase #6 $108.55   9.522%   $118.8861   $118.89   $118.90   $118.90  
  Purchase #7 $198.59   9.151%   $216.763   $216.76   $216.75   $216.80  
  7 purchase totals = $987.94       $1,077.3500   $1,077.36   $1,077.40   $1,077.50