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 $26.33   3.843%   $27.3419   $27.34   $27.35   $27.30  
  Purchase #2 $210.41   13.673%   $239.1794   $239.18   $239.20   $239.20  
  Purchase #3 $20.33   12.698%   $22.9115   $22.91   $22.90   $22.90  
  Purchase #4 $70.86   13.652%   $80.5338   $80.53   $80.55   $80.50  
  Purchase #5 $214.96   8.227%   $232.6448   $232.64   $232.65   $232.60  
  Purchase #6 $200.72   5.251%   $211.2598   $211.26   $211.25   $211.30  
  Purchase #7 $241.53   8.244%   $261.4417   $261.44   $261.45   $261.40  
  7 purchase totals = $985.14       $1,075.3129   $1,075.30   $1,075.35   $1,075.20