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	$47.26	6.449%	$50.3078	$50.31	$50.30	$50.30
Purchase #2	$234.42	10.132%	$258.1714	$258.17	$258.15	$258.20
Purchase #3	$50.32	7.548%	$54.1182	$54.12	$54.10	$54.10
Purchase #4	$84.25	11.741%	$94.1418	$94.14	$94.15	$94.10
Purchase #5	$152.99	10.770%	$169.467	$169.47	$169.45	$169.50
Purchase #6	$39.93	9.872%	$43.8719	$43.87	$43.85	$43.90
Purchase #7	$249.29	9.150%	$272.1	$272.10	$272.10	$272.10
7 purchase totals =	$858.46		$942.1781	$942.18	$942.10	$942.20