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	$132.52	13.857%	$150.8833	$150.88	$150.90	$150.90
Purchase #2	$52.69	13.300%	$59.6978	$59.70	$59.70	$59.70
Purchase #3	$206.49	4.716%	$216.2281	$216.23	$216.25	$216.20
Purchase #4	$79.87	5.596%	$84.3395	$84.34	$84.35	$84.30
Purchase #5	$152.68	13.140%	$172.7422	$172.74	$172.75	$172.70
Purchase #6	$235.98	11.662%	$263.5	$263.50	$263.50	$263.50
Purchase #7	$44.50	4.359%	$46.4398	$46.44	$46.45	$46.40
7 purchase totals =	$904.73		$993.8307	$993.83	$993.90	$993.70