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 $108.84   13.332%   $123.3505   $123.35   $123.35   $123.40  
  Purchase #2 $233.73   6.372%   $248.6233   $248.62   $248.60   $248.60  
  Purchase #3 $181.62   12.627%   $204.5532   $204.55   $204.55   $204.60  
  Purchase #4 $51.69   3.789%   $53.6485   $53.65   $53.65   $53.60  
  Purchase #5 $246.35   9.434%   $269.5907   $269.59   $269.60   $269.60  
  Purchase #6 $194.57   10.130%   $214.2799   $214.28   $214.30   $214.30  
  Purchase #7 $69.37   7.212%   $74.373   $74.37   $74.35   $74.40  
  7 purchase totals = $1,086.17       $1,188.4191   $1,188.41   $1,188.40   $1,188.50