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	$133.28	4.678%	$139.5148	$139.51	$139.50	$139.50
Purchase #2	$54.80	6.290%	$58.2469	$58.25	$58.25	$58.20
Purchase #3	$235.97	5.218%	$248.2829	$248.28	$248.30	$248.30
Purchase #4	$99.56	5.634%	$105.1692	$105.17	$105.15	$105.20
Purchase #5	$126.45	8.534%	$137.2412	$137.24	$137.25	$137.20
Purchase #6	$49.54	6.832%	$52.9246	$52.92	$52.90	$52.90
Purchase #7	$81.58	4.714%	$85.4257	$85.43	$85.45	$85.40
7 purchase totals =	$781.18		$826.8053	$826.80	$826.80	$826.70