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 $76.53   13.452%   $86.8248   $86.82   $86.80   $86.80  
  Purchase #2 $118.78   6.799%   $126.8559   $126.86   $126.85   $126.90  
  Purchase #3 $185.59   12.498%   $208.785   $208.79   $208.80   $208.80  
  Purchase #4 $146.93   11.642%   $164.0356   $164.04   $164.05   $164.00  
  Purchase #5 $219.74   3.211%   $226.7959   $226.80   $226.80   $226.80  
  Purchase #6 $31.90   4.596%   $33.3661   $33.37   $33.35   $33.40  
  Purchase #7 $239.60   4.741%   $250.9594   $250.96   $250.95   $251.00  
  7 purchase totals = $1,019.07       $1,097.6227   $1,097.64   $1,097.60   $1,097.70