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 $205.74   12.789%   $232.0521   $232.05   $232.05   $232.10  
  Purchase #2 $11.26   3.284%   $11.6298   $11.63   $11.65   $11.60  
  Purchase #3 $158.67   4.155%   $165.2627   $165.26   $165.25   $165.30  
  Purchase #4 $114.26   5.537%   $120.5866   $120.59   $120.60   $120.60  
  Purchase #5 $14.69   4.454%   $15.3443   $15.34   $15.35   $15.30  
  Purchase #6 $76.32   7.352%   $81.931   $81.93   $81.95   $81.90  
  Purchase #7 $141.55   3.440%   $146.4193   $146.42   $146.40   $146.40  
  7 purchase totals = $722.49       $773.2258   $773.22   $773.25   $773.20