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 $16.68   3.492%   $17.2625   $17.26   $17.25   $17.30  
  Purchase #2 $247.55   11.209%   $275.2979   $275.30   $275.30   $275.30  
  Purchase #3 $75.63   10.494%   $83.5666   $83.57   $83.55   $83.60  
  Purchase #4 $249.26   7.838%   $268.797   $268.80   $268.80   $268.80  
  Purchase #5 $122.54   12.321%   $137.6382   $137.64   $137.65   $137.60  
  Purchase #6 $134.32   4.436%   $140.2784   $140.28   $140.30   $140.30  
  Purchase #7 $34.45   13.441%   $39.0804   $39.08   $39.10   $39.10  
  7 purchase totals = $880.43       $961.9210   $961.93   $961.95   $962.00