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	$27.88	13.316%	$31.5925	$31.59	$31.60	$31.60
Purchase #2	$26.55	4.859%	$27.8401	$27.84	$27.85	$27.80
Purchase #3	$137.38	6.228%	$145.936	$145.94	$145.95	$145.90
Purchase #4	$73.54	11.852%	$82.256	$82.26	$82.25	$82.30
Purchase #5	$78.29	9.711%	$85.8927	$85.89	$85.90	$85.90
Purchase #6	$130.81	7.263%	$140.3107	$140.31	$140.30	$140.30
Purchase #7	$129.59	3.244%	$133.7939	$133.79	$133.80	$133.80
7 purchase totals =	$604.04		$647.6219	$647.62	$647.65	$647.60