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 $212.78   3.197%   $219.5826   $219.58   $219.60   $219.60  
  Purchase #2 $88.33   8.608%   $95.9334   $95.93   $95.95   $95.90  
  Purchase #3 $6.33   5.639%   $6.6869   $6.69   $6.70   $6.70  
  Purchase #4 $112.58   12.147%   $126.2551   $126.26   $126.25   $126.30  
  Purchase #5 $173.93   10.585%   $192.3405   $192.34   $192.35   $192.30  
  Purchase #6 $147.27   7.690%   $158.5951   $158.60   $158.60   $158.60  
  Purchase #7 $200.86   7.283%   $215.4886   $215.49   $215.50   $215.50  
  7 purchase totals = $942.08       $1,014.8822   $1,014.89   $1,014.95   $1,014.90