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 $182.50   12.763%   $205.7925   $205.79   $205.80   $205.80  
  Purchase #2 $52.66   9.255%   $57.5337   $57.53   $57.55   $57.50  
  Purchase #3 $55.43   11.265%   $61.6742   $61.67   $61.65   $61.70  
  Purchase #4 $239.48   10.346%   $264.2566   $264.26   $264.25   $264.30  
  Purchase #5 $7.82   10.489%   $8.6402   $8.64   $8.65   $8.60  
  Purchase #6 $186.43   12.806%   $210.3042   $210.30   $210.30   $210.30  
  Purchase #7 $156.39   12.749%   $176.3282   $176.33   $176.35   $176.30  
  7 purchase totals = $880.71       $984.5296   $984.52   $984.55   $984.50