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	$89.32	13.199%	$101.1093	$101.11	$101.10	$101.10
Purchase #2	$91.65	8.809%	$99.7234	$99.72	$99.70	$99.70
Purchase #3	$215.96	3.278%	$223.0392	$223.04	$223.05	$223.00
Purchase #4	$154.49	7.624%	$166.2683	$166.27	$166.25	$166.30
Purchase #5	$167.52	12.156%	$187.8837	$187.88	$187.90	$187.90
Purchase #6	$88.27	4.724%	$92.4399	$92.44	$92.45	$92.40
Purchase #7	$165.87	11.181%	$184.4159	$184.42	$184.40	$184.40
7 purchase totals =	$973.08		$1,054.8797	$1,054.88	$1,054.85	$1,054.80