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	$41.89	8.567%	$45.4787	$45.48	$45.50	$45.50
Purchase #2	$94.84	4.702%	$99.2994	$99.30	$99.30	$99.30
Purchase #3	$42.41	9.637%	$46.4971	$46.50	$46.50	$46.50
Purchase #4	$190.66	7.200%	$204.3875	$204.39	$204.40	$204.40
Purchase #5	$120.36	8.540%	$130.6387	$130.64	$130.65	$130.60
Purchase #6	$56.99	13.179%	$64.5007	$64.50	$64.50	$64.50
Purchase #7	$236.81	5.867%	$250.7036	$250.70	$250.70	$250.70
7 purchase totals =	$783.96		$841.5057	$841.51	$841.55	$841.50