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 $48.96   12.873%   $55.2626   $55.26   $55.25   $55.30  
  Purchase #2 $102.65   4.670%   $107.4438   $107.44   $107.45   $107.40  
  Purchase #3 $48.30   11.136%   $53.6787   $53.68   $53.70   $53.70  
  Purchase #4 $40.71   11.232%   $45.2825   $45.28   $45.30   $45.30  
  Purchase #5 $233.32   11.784%   $260.8144   $260.81   $260.80   $260.80  
  Purchase #6 $205.53   10.437%   $226.9812   $226.98   $227.00   $227.00  
  Purchase #7 $187.74   13.679%   $213.421   $213.42   $213.40   $213.40  
  7 purchase totals = $867.21       $962.8842   $962.87   $962.90   $962.90