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 $37.57   11.325%   $41.8248   $41.82   $41.80   $41.80  
  Purchase #2 $243.66   8.326%   $263.9471   $263.95   $263.95   $263.90  
  Purchase #3 $86.26   9.780%   $94.6962   $94.70   $94.70   $94.70  
  Purchase #4 $184.78   11.422%   $205.8856   $205.89   $205.90   $205.90  
  Purchase #5 $48.43   10.304%   $53.4202   $53.42   $53.40   $53.40  
  Purchase #6 $64.62   8.127%   $69.8717   $69.87   $69.85   $69.90  
  Purchase #7 $109.81   5.839%   $116.2218   $116.22   $116.20   $116.20  
  7 purchase totals = $775.13       $845.8674   $845.87   $845.80   $845.80