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	$28.51	3.541%	$29.5195	$29.52	$29.50	$29.50
Purchase #2	$235.45	9.713%	$258.3193	$258.32	$258.30	$258.30
Purchase #3	$98.84	11.364%	$110.0722	$110.07	$110.05	$110.10
Purchase #4	$57.76	12.333%	$64.8835	$64.88	$64.90	$64.90
Purchase #5	$89.49	12.626%	$100.789	$100.79	$100.80	$100.80
Purchase #6	$157.47	9.442%	$172.3383	$172.34	$172.35	$172.30
Purchase #7	$109.42	10.105%	$120.4769	$120.48	$120.50	$120.50
7 purchase totals =	$776.94		$856.3987	$856.40	$856.40	$856.40