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	$101.35	8.332%	$109.7945	$109.79	$109.80	$109.80
Purchase #2	$120.42	5.815%	$127.4224	$127.42	$127.40	$127.40
Purchase #3	$159.42	10.343%	$175.9088	$175.91	$175.90	$175.90
Purchase #4	$10.52	6.151%	$11.1671	$11.17	$11.15	$11.20
Purchase #5	$160.85	12.615%	$181.1412	$181.14	$181.15	$181.10
Purchase #6	$39.54	3.179%	$40.797	$40.80	$40.80	$40.80
Purchase #7	$141.95	9.516%	$155.458	$155.46	$155.45	$155.50
7 purchase totals =	$734.05		$801.6890	$801.69	$801.65	$801.70