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	$19.68	4.468%	$20.5593	$20.56	$20.55	$20.60
Purchase #2	$199.64	11.701%	$222.9999	$223.00	$223.00	$223.00
Purchase #3	$146.57	12.855%	$165.4116	$165.41	$165.40	$165.40
Purchase #4	$240.52	9.477%	$263.3141	$263.31	$263.30	$263.30
Purchase #5	$56.29	5.872%	$59.5953	$59.60	$59.60	$59.60
Purchase #6	$128.56	12.400%	$144.5014	$144.50	$144.50	$144.50
Purchase #7	$26.31	12.368%	$29.564	$29.56	$29.55	$29.60
7 purchase totals =	$817.57		$905.9456	$905.94	$905.90	$906.00