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 $249.96   7.324%   $268.2671   $268.27   $268.25   $268.30  
  Purchase #2 $143.54   12.862%   $162.0021   $162.00   $162.00   $162.00  
  Purchase #3 $47.83   7.837%   $51.5784   $51.58   $51.60   $51.60  
  Purchase #4 $216.84   7.612%   $233.3459   $233.35   $233.35   $233.30  
  Purchase #5 $192.44   4.388%   $200.8843   $200.88   $200.90   $200.90  
  Purchase #6 $179.39   8.415%   $194.4857   $194.49   $194.50   $194.50  
  Purchase #7 $71.27   12.863%   $80.4375   $80.44   $80.45   $80.40  
  7 purchase totals = $1,101.27       $1,191.0010   $1,191.01   $1,191.05   $1,191.00