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 $70.89   5.554%   $74.8272   $74.83   $74.85   $74.80  
  Purchase #2 $97.70   4.181%   $101.7848   $101.78   $101.80   $101.80  
  Purchase #3 $230.74   9.461%   $252.5703   $252.57   $252.55   $252.60  
  Purchase #4 $81.63   5.673%   $86.2609   $86.26   $86.25   $86.30  
  Purchase #5 $118.80   10.128%   $130.8321   $130.83   $130.85   $130.80  
  Purchase #6 $167.54   3.263%   $173.0068   $173.01   $173.00   $173.00  
  Purchase #7 $216.35   12.857%   $244.1661   $244.17   $244.15   $244.20  
  7 purchase totals = $983.65       $1,063.4482   $1,063.45   $1,063.45   $1,063.50