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	$165.53	3.465%	$171.2656	$171.27	$171.25	$171.30
Purchase #2	$150.31	10.202%	$165.6446	$165.64	$165.65	$165.60
Purchase #3	$88.51	11.150%	$98.3789	$98.38	$98.40	$98.40
Purchase #4	$216.97	8.540%	$235.4992	$235.50	$235.50	$235.50
Purchase #5	$146.31	13.166%	$165.5732	$165.57	$165.55	$165.60
Purchase #6	$105.89	9.685%	$116.1454	$116.15	$116.15	$116.10
Purchase #7	$51.54	10.488%	$56.9455	$56.95	$56.95	$56.90
7 purchase totals =	$925.06		$1,009.4524	$1,009.46	$1,009.45	$1,009.40