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	$55.52	9.721%	$60.9171	$60.92	$60.90	$60.90
Purchase #2	$49.80	5.427%	$52.5026	$52.50	$52.50	$52.50
Purchase #3	$37.87	7.550%	$40.7292	$40.73	$40.75	$40.70
Purchase #4	$205.49	9.522%	$225.0568	$225.06	$225.05	$225.10
Purchase #5	$76.94	12.198%	$86.3251	$86.33	$86.35	$86.30
Purchase #6	$192.92	10.864%	$213.8788	$213.88	$213.90	$213.90
Purchase #7	$56.31	5.729%	$59.536	$59.54	$59.55	$59.50
7 purchase totals =	$674.85		$738.9456	$738.96	$739.00	$738.90