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	$93.39	6.511%	$99.4706	$99.47	$99.45	$99.50
Purchase #2	$127.51	3.391%	$131.8339	$131.83	$131.85	$131.80
Purchase #3	$77.73	13.396%	$88.1427	$88.14	$88.15	$88.10
Purchase #4	$175.54	12.559%	$197.5861	$197.59	$197.60	$197.60
Purchase #5	$221.96	7.259%	$238.0721	$238.07	$238.05	$238.10
Purchase #6	$73.66	12.163%	$82.6193	$82.62	$82.60	$82.60
Purchase #7	$161.65	7.863%	$174.3605	$174.36	$174.35	$174.40
7 purchase totals =	$931.44		$1,012.0852	$1,012.08	$1,012.05	$1,012.10