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 $196.28   9.278%   $214.4909   $214.49   $214.50   $214.50  
  Purchase #2 $78.92   10.184%   $86.9572   $86.96   $86.95   $87.00  
  Purchase #3 $92.77   6.609%   $98.9012   $98.90   $98.90   $98.90  
  Purchase #4 $121.79   9.674%   $133.572   $133.57   $133.55   $133.60  
  Purchase #5 $237.61   13.607%   $269.9416   $269.94   $269.95   $269.90  
  Purchase #6 $38.59   8.628%   $41.9195   $41.92   $41.90   $41.90  
  Purchase #7 $200.81   6.772%   $214.4089   $214.41   $214.40   $214.40  
  7 purchase totals = $966.77       $1,060.1913   $1,060.19   $1,060.15   $1,060.20