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 $153.91   6.687%   $164.202   $164.20   $164.20   $164.20  
  Purchase #2 $201.90   3.362%   $208.6879   $208.69   $208.70   $208.70  
  Purchase #3 $78.63   5.598%   $83.0317   $83.03   $83.05   $83.00  
  Purchase #4 $202.41   11.552%   $225.7924   $225.79   $225.80   $225.80  
  Purchase #5 $50.90   4.273%   $53.075   $53.08   $53.10   $53.10  
  Purchase #6 $174.83   5.309%   $184.1117   $184.11   $184.10   $184.10  
  Purchase #7 $211.97   11.620%   $236.6009   $236.60   $236.60   $236.60  
  7 purchase totals = $1,074.55       $1,155.5016   $1,155.50   $1,155.55   $1,155.50