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 $79.89   7.873%   $86.1797   $86.18   $86.20   $86.20  
  Purchase #2 $148.74   9.277%   $162.5386   $162.54   $162.55   $162.50  
  Purchase #3 $139.26   9.674%   $152.732   $152.73   $152.75   $152.70  
  Purchase #4 $100.31   4.871%   $105.1961   $105.20   $105.20   $105.20  
  Purchase #5 $192.79   5.259%   $202.9288   $202.93   $202.95   $202.90  
  Purchase #6 $216.69   3.753%   $224.8224   $224.82   $224.80   $224.80  
  Purchase #7 $214.44   5.623%   $226.498   $226.50   $226.50   $226.50  
  7 purchase totals = $1,092.12       $1,160.8956   $1,160.90   $1,160.95   $1,160.80