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 $244.48   7.405%   $262.5837   $262.58   $262.60   $262.60  
  Purchase #2 $109.70   6.636%   $116.9797   $116.98   $117.00   $117.00  
  Purchase #3 $87.77   6.534%   $93.5049   $93.50   $93.50   $93.50  
  Purchase #4 $201.44   6.577%   $214.6887   $214.69   $214.70   $214.70  
  Purchase #5 $219.33   9.170%   $239.4426   $239.44   $239.45   $239.40  
  Purchase #6 $223.37   11.373%   $248.7739   $248.77   $248.75   $248.80  
  Purchase #7 $83.81   12.783%   $94.5234   $94.52   $94.50   $94.50  
  7 purchase totals = $1,169.90       $1,270.4969   $1,270.48   $1,270.50   $1,270.50