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	$108.82	9.270%	$118.9076	$118.91	$118.90	$118.90
Purchase #2	$62.57	9.406%	$68.4553	$68.46	$68.45	$68.50
Purchase #3	$148.33	11.615%	$165.5585	$165.56	$165.55	$165.60
Purchase #4	$107.91	9.507%	$118.169	$118.17	$118.15	$118.20
Purchase #5	$126.95	3.592%	$131.51	$131.51	$131.50	$131.50
Purchase #6	$52.27	7.514%	$56.1976	$56.20	$56.20	$56.20
Purchase #7	$136.80	8.567%	$148.5197	$148.52	$148.50	$148.50
7 purchase totals =	$743.65		$807.3177	$807.33	$807.25	$807.40