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	$181.30	13.681%	$206.1037	$206.10	$206.10	$206.10
Purchase #2	$49.29	6.476%	$52.482	$52.48	$52.50	$52.50
Purchase #3	$91.91	8.830%	$100.0257	$100.03	$100.05	$100.00
Purchase #4	$195.43	4.656%	$204.5292	$204.53	$204.55	$204.50
Purchase #5	$43.33	11.874%	$48.475	$48.48	$48.50	$48.50
Purchase #6	$62.73	10.157%	$69.1015	$69.10	$69.10	$69.10
Purchase #7	$152.76	13.152%	$172.851	$172.85	$172.85	$172.90
7 purchase totals =	$776.75		$853.5681	$853.57	$853.65	$853.60