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 $183.70   11.423%   $204.6841   $204.68   $204.70   $204.70  
  Purchase #2 $111.63   4.248%   $116.372   $116.37   $116.35   $116.40  
  Purchase #3 $122.67   6.669%   $130.8509   $130.85   $130.85   $130.90  
  Purchase #4 $175.73   5.496%   $185.3881   $185.39   $185.40   $185.40  
  Purchase #5 $246.96   3.608%   $255.8703   $255.87   $255.85   $255.90  
  Purchase #6 $34.79   9.216%   $37.9962   $38.00   $38.00   $38.00  
  Purchase #7 $40.62   9.750%   $44.5805   $44.58   $44.60   $44.60  
  7 purchase totals = $916.10       $975.7421   $975.74   $975.75   $975.90