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 $205.95   13.751%   $234.2702   $234.27   $234.25   $234.30  
  Purchase #2 $90.95   5.473%   $95.9277   $95.93   $95.95   $95.90  
  Purchase #3 $136.94   12.689%   $154.3163   $154.32   $154.30   $154.30  
  Purchase #4 $97.26   12.578%   $109.4934   $109.49   $109.50   $109.50  
  Purchase #5 $56.97   8.398%   $61.7543   $61.75   $61.75   $61.80  
  Purchase #6 $126.88   8.247%   $137.3438   $137.34   $137.35   $137.30  
  Purchase #7 $47.46   13.490%   $53.8624   $53.86   $53.85   $53.90  
  7 purchase totals = $762.41       $846.9681   $846.96   $846.95   $847.00