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 $62.93   8.283%   $68.1425   $68.14   $68.15   $68.10  
  Purchase #2 $73.74   13.856%   $83.9574   $83.96   $83.95   $84.00  
  Purchase #3 $103.44   10.756%   $114.566   $114.57   $114.55   $114.60  
  Purchase #4 $119.70   9.202%   $130.7148   $130.71   $130.70   $130.70  
  Purchase #5 $238.69   9.159%   $260.5516   $260.55   $260.55   $260.60  
  Purchase #6 $38.25   5.531%   $40.3656   $40.37   $40.35   $40.40  
  Purchase #7 $203.92   7.569%   $219.3547   $219.35   $219.35   $219.40  
  7 purchase totals = $840.67       $917.6526   $917.65   $917.60   $917.80