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 $149.32   13.731%   $169.8231   $169.82   $169.80   $169.80  
  Purchase #2 $93.58   6.176%   $99.3595   $99.36   $99.35   $99.40  
  Purchase #3 $60.78   4.436%   $63.4762   $63.48   $63.50   $63.50  
  Purchase #4 $139.76   12.591%   $157.3572   $157.36   $157.35   $157.40  
  Purchase #5 $219.36   8.529%   $238.0692   $238.07   $238.05   $238.10  
  Purchase #6 $206.43   8.874%   $224.7486   $224.75   $224.75   $224.70  
  Purchase #7 $115.42   6.175%   $122.5472   $122.55   $122.55   $122.50  
  7 purchase totals = $984.65       $1,075.3810   $1,075.39   $1,075.35   $1,075.40