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	$61.68	4.610%	$64.5234	$64.52	$64.50	$64.50
Purchase #2	$121.37	8.362%	$131.519	$131.52	$131.50	$131.50
Purchase #3	$56.59	6.316%	$60.1642	$60.16	$60.15	$60.20
Purchase #4	$158.91	13.289%	$180.0275	$180.03	$180.05	$180.00
Purchase #5	$24.75	13.278%	$28.0363	$28.04	$28.05	$28.00
Purchase #6	$86.59	4.176%	$90.206	$90.21	$90.20	$90.20
Purchase #7	$22.31	11.404%	$24.8542	$24.85	$24.85	$24.90
7 purchase totals =	$532.20		$579.3306	$579.33	$579.30	$579.30