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	$236.34	4.724%	$247.5047	$247.50	$247.50	$247.50
Purchase #2	$76.56	12.736%	$86.3107	$86.31	$86.30	$86.30
Purchase #3	$115.30	10.479%	$127.3823	$127.38	$127.40	$127.40
Purchase #4	$249.36	12.562%	$280.6846	$280.68	$280.70	$280.70
Purchase #5	$61.99	5.242%	$65.2395	$65.24	$65.25	$65.20
Purchase #6	$64.89	12.292%	$72.8663	$72.87	$72.85	$72.90
Purchase #7	$122.69	11.820%	$137.192	$137.19	$137.20	$137.20
7 purchase totals =	$927.13		$1,017.1801	$1,017.17	$1,017.20	$1,017.20