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	$179.37	6.532%	$191.0864	$191.09	$191.10	$191.10
Purchase #2	$79.65	12.209%	$89.3745	$89.37	$89.35	$89.40
Purchase #3	$192.39	8.149%	$208.0679	$208.07	$208.05	$208.10
Purchase #4	$62.68	13.111%	$70.898	$70.90	$70.90	$70.90
Purchase #5	$78.59	7.742%	$84.6744	$84.67	$84.65	$84.70
Purchase #6	$96.89	3.757%	$100.5302	$100.53	$100.55	$100.50
Purchase #7	$102.76	3.492%	$106.3484	$106.35	$106.35	$106.30
7 purchase totals =	$792.33		$850.9798	$850.98	$850.95	$851.00