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	$160.78	11.824%	$179.7906	$179.79	$179.80	$179.80
Purchase #2	$80.53	10.281%	$88.8093	$88.81	$88.80	$88.80
Purchase #3	$186.57	3.213%	$192.5645	$192.56	$192.55	$192.60
Purchase #4	$133.39	3.841%	$138.5135	$138.51	$138.50	$138.50
Purchase #5	$129.40	8.300%	$140.1402	$140.14	$140.15	$140.10
Purchase #6	$158.42	8.855%	$172.4481	$172.45	$172.45	$172.40
Purchase #7	$118.61	7.791%	$127.8509	$127.85	$127.85	$127.90
7 purchase totals =	$967.70		$1,040.1171	$1,040.11	$1,040.10	$1,040.10