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	$246.46	13.376%	$279.4265	$279.43	$279.45	$279.40
Purchase #2	$124.74	9.635%	$136.7587	$136.76	$136.75	$136.80
Purchase #3	$152.67	3.763%	$158.415	$158.42	$158.40	$158.40
Purchase #4	$65.59	11.294%	$72.9977	$73.00	$73.00	$73.00
Purchase #5	$25.48	4.109%	$26.527	$26.53	$26.55	$26.50
Purchase #6	$201.85	7.286%	$216.5568	$216.56	$216.55	$216.60
Purchase #7	$106.50	4.526%	$111.3202	$111.32	$111.30	$111.30
7 purchase totals =	$923.29		$1,002.0019	$1,002.02	$1,002.00	$1,002.00