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 $24.57   9.348%   $26.8668   $26.87   $26.85   $26.90  
  Purchase #2 $135.50   8.362%   $146.8305   $146.83   $146.85   $146.80  
  Purchase #3 $164.54   3.131%   $169.6917   $169.69   $169.70   $169.70  
  Purchase #4 $165.74   10.704%   $183.4808   $183.48   $183.50   $183.50  
  Purchase #5 $198.96   5.305%   $209.5148   $209.51   $209.50   $209.50  
  Purchase #6 $159.55   3.125%   $164.5359   $164.54   $164.55   $164.50  
  Purchase #7 $139.92   9.743%   $153.5524   $153.55   $153.55   $153.60  
  7 purchase totals = $988.78       $1,054.4729   $1,054.47   $1,054.50   $1,054.50