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	$51.53	5.268%	$54.2446	$54.24	$54.25	$54.20
Purchase #2	$68.67	13.504%	$77.9432	$77.94	$77.95	$77.90
Purchase #3	$225.27	10.672%	$249.3108	$249.31	$249.30	$249.30
Purchase #4	$55.33	7.351%	$59.3973	$59.40	$59.40	$59.40
Purchase #5	$17.52	9.313%	$19.1516	$19.15	$19.15	$19.20
Purchase #6	$87.43	6.123%	$92.7833	$92.78	$92.80	$92.80
Purchase #7	$165.68	8.238%	$179.3287	$179.33	$179.35	$179.30
7 purchase totals =	$671.43		$732.1595	$732.15	$732.20	$732.10