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 $53.92   12.497%   $60.6584   $60.66   $60.65   $60.70  
  Purchase #2 $172.93   13.175%   $195.7135   $195.71   $195.70   $195.70  
  Purchase #3 $220.40   7.437%   $236.7911   $236.79   $236.80   $236.80  
  Purchase #4 $86.38   13.287%   $97.8573   $97.86   $97.85   $97.90  
  Purchase #5 $69.67   9.675%   $76.4106   $76.41   $76.40   $76.40  
  Purchase #6 $184.62   12.864%   $208.3695   $208.37   $208.35   $208.40  
  Purchase #7 $200.79   6.613%   $214.0682   $214.07   $214.05   $214.10  
  7 purchase totals = $988.71       $1,089.8686   $1,089.87   $1,089.80   $1,090.00