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	$203.69	6.650%	$217.2354	$217.24	$217.25	$217.20
Purchase #2	$138.75	8.330%	$150.3079	$150.31	$150.30	$150.30
Purchase #3	$50.67	13.443%	$57.4816	$57.48	$57.50	$57.50
Purchase #4	$83.72	6.446%	$89.1166	$89.12	$89.10	$89.10
Purchase #5	$131.50	10.118%	$144.8052	$144.81	$144.80	$144.80
Purchase #6	$8.93	7.842%	$9.6303	$9.63	$9.65	$9.60
Purchase #7	$249.66	10.164%	$275.0354	$275.04	$275.05	$275.00
7 purchase totals =	$866.92		$943.6124	$943.63	$943.65	$943.50