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	$155.89	8.176%	$168.6356	$168.64	$168.65	$168.60
Purchase #2	$99.33	11.614%	$110.8662	$110.87	$110.85	$110.90
Purchase #3	$157.96	13.381%	$179.0966	$179.10	$179.10	$179.10
Purchase #4	$167.48	12.162%	$187.8489	$187.85	$187.85	$187.80
Purchase #5	$70.83	12.604%	$79.7574	$79.76	$79.75	$79.80
Purchase #6	$37.62	12.239%	$42.2243	$42.22	$42.20	$42.20
Purchase #7	$34.74	9.713%	$38.1143	$38.11	$38.10	$38.10
7 purchase totals =	$723.85		$806.5433	$806.55	$806.50	$806.50