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	$92.92	8.178%	$100.519	$100.52	$100.50	$100.50
Purchase #2	$69.90	3.650%	$72.4514	$72.45	$72.45	$72.50
Purchase #3	$123.59	6.247%	$131.3107	$131.31	$131.30	$131.30
Purchase #4	$119.74	12.807%	$135.0751	$135.08	$135.10	$135.10
Purchase #5	$118.51	10.426%	$130.8659	$130.87	$130.85	$130.90
Purchase #6	$81.56	11.378%	$90.8399	$90.84	$90.85	$90.80
Purchase #7	$42.41	8.772%	$46.1302	$46.13	$46.15	$46.10
7 purchase totals =	$648.63		$707.1922	$707.20	$707.20	$707.20