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 $52.55   7.613%   $56.5506   $56.55   $56.55   $56.60  
  Purchase #2 $197.75   3.748%   $205.1617   $205.16   $205.15   $205.20  
  Purchase #3 $19.63   13.625%   $22.3046   $22.30   $22.30   $22.30  
  Purchase #4 $141.88   12.357%   $159.4121   $159.41   $159.40   $159.40  
  Purchase #5 $197.70   6.405%   $210.3627   $210.36   $210.35   $210.40  
  Purchase #6 $65.53   8.554%   $71.1354   $71.14   $71.15   $71.10  
  Purchase #7 $206.92   12.611%   $233.0147   $233.01   $233.00   $233.00  
  7 purchase totals = $881.96       $957.9418   $957.93   $957.90   $958.00