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	$234.69	9.196%	$256.2721	$256.27	$256.25	$256.30
Purchase #2	$39.65	9.814%	$43.5413	$43.54	$43.55	$43.50
Purchase #3	$201.50	8.234%	$218.0915	$218.09	$218.10	$218.10
Purchase #4	$169.67	13.110%	$191.9137	$191.91	$191.90	$191.90
Purchase #5	$82.87	8.286%	$89.7366	$89.74	$89.75	$89.70
Purchase #6	$229.79	13.103%	$259.8994	$259.90	$259.90	$259.90
Purchase #7	$6.40	4.499%	$6.6879	$6.69	$6.70	$6.70
7 purchase totals =	$964.57		$1,066.1425	$1,066.14	$1,066.15	$1,066.10