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	$33.71	5.266%	$35.4852	$35.49	$35.50	$35.50
Purchase #2	$129.46	6.494%	$137.8671	$137.87	$137.85	$137.90
Purchase #3	$109.56	3.283%	$113.1569	$113.16	$113.15	$113.20
Purchase #4	$142.82	7.342%	$153.3058	$153.31	$153.30	$153.30
Purchase #5	$120.90	4.374%	$126.1882	$126.19	$126.20	$126.20
Purchase #6	$117.57	11.466%	$131.0506	$131.05	$131.05	$131.10
Purchase #7	$243.98	11.531%	$272.1133	$272.11	$272.10	$272.10
7 purchase totals =	$898.00		$969.1671	$969.18	$969.15	$969.30