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 $233.81   5.545%   $246.7748   $246.77   $246.75   $246.80  
  Purchase #2 $35.64   4.135%   $37.1137   $37.11   $37.10   $37.10  
  Purchase #3 $53.90   5.314%   $56.7642   $56.76   $56.75   $56.80  
  Purchase #4 $91.77   9.186%   $100.2   $100.20   $100.20   $100.20  
  Purchase #5 $21.25   6.478%   $22.6266   $22.63   $22.65   $22.60  
  Purchase #6 $240.98   11.841%   $269.5144   $269.51   $269.50   $269.50  
  Purchase #7 $163.29   5.753%   $172.6841   $172.68   $172.70   $172.70  
  7 purchase totals = $840.64       $905.6778   $905.66   $905.65   $905.70