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	$183.40	3.256%	$189.3715	$189.37	$189.35	$189.40
Purchase #2	$199.82	11.594%	$222.9871	$222.99	$223.00	$223.00
Purchase #3	$44.60	4.688%	$46.6908	$46.69	$46.70	$46.70
Purchase #4	$179.64	6.690%	$191.6579	$191.66	$191.65	$191.70
Purchase #5	$248.77	5.254%	$261.8404	$261.84	$261.85	$261.80
Purchase #6	$72.59	9.158%	$79.2378	$79.24	$79.25	$79.20
Purchase #7	$87.90	13.686%	$99.93	$99.93	$99.95	$99.90
7 purchase totals =	$1,016.72		$1,091.7155	$1,091.72	$1,091.75	$1,091.70