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	$91.67	8.336%	$99.3116	$99.31	$99.30	$99.30
Purchase #2	$72.73	13.780%	$82.7522	$82.75	$82.75	$82.80
Purchase #3	$74.89	4.509%	$78.2668	$78.27	$78.25	$78.30
Purchase #4	$172.77	11.362%	$192.4001	$192.40	$192.40	$192.40
Purchase #5	$47.72	11.481%	$53.1987	$53.20	$53.20	$53.20
Purchase #6	$70.75	11.499%	$78.8855	$78.89	$78.90	$78.90
Purchase #7	$47.77	6.859%	$51.0465	$51.05	$51.05	$51.00
7 purchase totals =	$578.30		$635.8614	$635.87	$635.85	$635.90