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	$83.92	9.133%	$91.5844	$91.58	$91.60	$91.60
Purchase #2	$120.37	12.758%	$135.7268	$135.73	$135.75	$135.70
Purchase #3	$229.54	9.118%	$250.4695	$250.47	$250.45	$250.50
Purchase #4	$211.55	5.322%	$222.8087	$222.81	$222.80	$222.80
Purchase #5	$127.39	13.357%	$144.4055	$144.41	$144.40	$144.40
Purchase #6	$125.83	10.743%	$139.3479	$139.35	$139.35	$139.30
Purchase #7	$220.46	8.139%	$238.4032	$238.40	$238.40	$238.40
7 purchase totals =	$1,119.06		$1,222.7460	$1,222.75	$1,222.75	$1,222.70