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 $53.62   13.356%   $60.7815   $60.78   $60.80   $60.80  
  Purchase #2 $176.87   5.688%   $186.9304   $186.93   $186.95   $186.90  
  Purchase #3 $14.28   6.753%   $15.2443   $15.24   $15.25   $15.20  
  Purchase #4 $196.36   12.733%   $221.3625   $221.36   $221.35   $221.40  
  Purchase #5 $101.26   9.186%   $110.5617   $110.56   $110.55   $110.60  
  Purchase #6 $98.26   7.587%   $105.715   $105.72   $105.70   $105.70  
  Purchase #7 $249.41   10.122%   $274.6553   $274.66   $274.65   $274.70  
  7 purchase totals = $890.06       $975.2507   $975.25   $975.25   $975.30