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 $83.80   12.831%   $94.5524   $94.55   $94.55   $94.60  
  Purchase #2 $91.57   7.316%   $98.2693   $98.27   $98.25   $98.30  
  Purchase #3 $188.60   6.416%   $200.7006   $200.70   $200.70   $200.70  
  Purchase #4 $119.98   5.119%   $126.1218   $126.12   $126.10   $126.10  
  Purchase #5 $159.70   3.863%   $165.8692   $165.87   $165.85   $165.90  
  Purchase #6 $120.25   13.851%   $136.9058   $136.91   $136.90   $136.90  
  Purchase #7 $11.37   10.751%   $12.5924   $12.59   $12.60   $12.60  
  7 purchase totals = $775.27       $835.0115   $835.01   $834.95   $835.10