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	$85.44	5.282%	$89.9529	$89.95	$89.95	$90.00
Purchase #2	$40.29	13.536%	$45.7437	$45.74	$45.75	$45.70
Purchase #3	$19.77	8.722%	$21.4943	$21.49	$21.50	$21.50
Purchase #4	$25.79	4.199%	$26.8729	$26.87	$26.85	$26.90
Purchase #5	$101.25	4.643%	$105.951	$105.95	$105.95	$106.00
Purchase #6	$89.59	13.283%	$101.4902	$101.49	$101.50	$101.50
Purchase #7	$179.98	9.367%	$196.8387	$196.84	$196.85	$196.80
7 purchase totals =	$542.11		$588.3437	$588.33	$588.35	$588.40