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	$155.36	9.203%	$169.6578	$169.66	$169.65	$169.70
Purchase #2	$43.74	4.650%	$45.7739	$45.77	$45.75	$45.80
Purchase #3	$25.47	10.552%	$28.1576	$28.16	$28.15	$28.20
Purchase #4	$86.31	7.180%	$92.5071	$92.51	$92.50	$92.50
Purchase #5	$28.28	10.738%	$31.3167	$31.32	$31.30	$31.30
Purchase #6	$146.69	12.702%	$165.3226	$165.32	$165.30	$165.30
Purchase #7	$222.36	11.648%	$248.2605	$248.26	$248.25	$248.30
7 purchase totals =	$708.21		$780.9962	$781.00	$780.90	$781.10