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 $118.74   6.471%   $126.4237   $126.42   $126.40   $126.40  
  Purchase #2 $164.48   5.845%   $174.0939   $174.09   $174.10   $174.10  
  Purchase #3 $233.34   4.356%   $243.5043   $243.50   $243.50   $243.50  
  Purchase #4 $160.49   10.230%   $176.9081   $176.91   $176.90   $176.90  
  Purchase #5 $201.75   7.367%   $216.6129   $216.61   $216.60   $216.60  
  Purchase #6 $240.48   12.468%   $270.463   $270.46   $270.45   $270.50  
  Purchase #7 $165.60   8.317%   $179.373   $179.37   $179.35   $179.40  
  7 purchase totals = $1,284.88       $1,387.3789   $1,387.36   $1,387.30   $1,387.40