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	$87.46	3.119%	$90.1879	$90.19	$90.20	$90.20
Purchase #2	$64.75	4.756%	$67.8295	$67.83	$67.85	$67.80
Purchase #3	$240.43	4.148%	$250.403	$250.40	$250.40	$250.40
Purchase #4	$68.49	9.336%	$74.8842	$74.88	$74.90	$74.90
Purchase #5	$238.56	8.228%	$258.1887	$258.19	$258.20	$258.20
Purchase #6	$172.75	7.410%	$185.5508	$185.55	$185.55	$185.60
Purchase #7	$209.42	6.613%	$223.2689	$223.27	$223.25	$223.30
7 purchase totals =	$1,081.86		$1,150.3130	$1,150.31	$1,150.35	$1,150.40