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	$122.66	7.476%	$131.8301	$131.83	$131.85	$131.80
Purchase #2	$216.25	4.209%	$225.352	$225.35	$225.35	$225.40
Purchase #3	$176.72	3.640%	$183.1526	$183.15	$183.15	$183.20
Purchase #4	$19.62	5.374%	$20.6744	$20.67	$20.65	$20.70
Purchase #5	$53.81	5.684%	$56.8686	$56.87	$56.85	$56.90
Purchase #6	$159.42	5.478%	$168.153	$168.15	$168.15	$168.20
Purchase #7	$55.28	6.458%	$58.85	$58.85	$58.85	$58.90
7 purchase totals =	$803.76		$844.8807	$844.87	$844.85	$845.10