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	$91.79	9.240%	$100.2714	$100.27	$100.25	$100.30
Purchase #2	$36.67	7.672%	$39.4833	$39.48	$39.50	$39.50
Purchase #3	$56.41	12.276%	$63.3349	$63.33	$63.35	$63.30
Purchase #4	$57.56	8.726%	$62.5827	$62.58	$62.60	$62.60
Purchase #5	$124.68	12.219%	$139.9146	$139.91	$139.90	$139.90
Purchase #6	$17.60	11.285%	$19.5862	$19.59	$19.60	$19.60
Purchase #7	$233.69	8.432%	$253.3947	$253.39	$253.40	$253.40
7 purchase totals =	$618.40		$678.5678	$678.55	$678.60	$678.60