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	$9.55	10.143%	$10.5187	$10.52	$10.50	$10.50
Purchase #2	$93.72	12.457%	$105.3947	$105.39	$105.40	$105.40
Purchase #3	$111.25	9.404%	$121.712	$121.71	$121.70	$121.70
Purchase #4	$165.76	9.384%	$181.3149	$181.31	$181.30	$181.30
Purchase #5	$209.89	11.148%	$233.2885	$233.29	$233.30	$233.30
Purchase #6	$86.81	7.668%	$93.4666	$93.47	$93.45	$93.50
Purchase #7	$234.78	5.538%	$247.7821	$247.78	$247.80	$247.80
7 purchase totals =	$911.76		$993.4775	$993.47	$993.45	$993.50