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 $84.78   12.841%   $95.6666   $95.67   $95.65   $95.70  
  Purchase #2 $169.52   12.537%   $190.7727   $190.77   $190.75   $190.80  
  Purchase #3 $219.40   9.335%   $239.881   $239.88   $239.90   $239.90  
  Purchase #4 $238.47   11.824%   $266.6667   $266.67   $266.65   $266.70  
  Purchase #5 $192.26   9.403%   $210.3382   $210.34   $210.35   $210.30  
  Purchase #6 $237.68   7.128%   $254.6218   $254.62   $254.60   $254.60  
  Purchase #7 $15.25   3.628%   $15.8033   $15.80   $15.80   $15.80  
  7 purchase totals = $1,157.36       $1,273.7503   $1,273.75   $1,273.70   $1,273.80