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 $58.45   10.722%   $64.717   $64.72   $64.70   $64.70  
  Purchase #2 $23.96   12.373%   $26.9246   $26.92   $26.90   $26.90  
  Purchase #3 $164.60   4.142%   $171.4177   $171.42   $171.40   $171.40  
  Purchase #4 $196.97   8.383%   $213.482   $213.48   $213.50   $213.50  
  Purchase #5 $172.43   11.720%   $192.6388   $192.64   $192.65   $192.60  
  Purchase #6 $39.58   11.862%   $44.275   $44.28   $44.30   $44.30  
  Purchase #7 $187.42   3.497%   $193.9741   $193.97   $193.95   $194.00  
  7 purchase totals = $843.41       $907.4292   $907.43   $907.40   $907.40