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 $183.47   7.211%   $196.7   $196.70   $196.70   $196.70  
  Purchase #2 $12.55   9.157%   $13.6992   $13.70   $13.70   $13.70  
  Purchase #3 $250.40   10.607%   $276.9599   $276.96   $276.95   $277.00  
  Purchase #4 $241.51   13.711%   $274.6234   $274.62   $274.60   $274.60  
  Purchase #5 $247.36   10.361%   $272.989   $272.99   $273.00   $273.00  
  Purchase #6 $239.54   4.769%   $250.9637   $250.96   $250.95   $251.00  
  Purchase #7 $218.42   13.487%   $247.8783   $247.88   $247.90   $247.90  
  7 purchase totals = $1,393.25       $1,533.8135   $1,533.81   $1,533.80   $1,533.90