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	$231.38	7.380%	$248.4558	$248.46	$248.45	$248.50
Purchase #2	$189.54	8.408%	$205.4765	$205.48	$205.50	$205.50
Purchase #3	$99.31	13.413%	$112.6305	$112.63	$112.65	$112.60
Purchase #4	$93.86	3.194%	$96.8579	$96.86	$96.85	$96.90
Purchase #5	$184.96	10.301%	$204.0127	$204.01	$204.00	$204.00
Purchase #6	$49.77	13.282%	$56.3805	$56.38	$56.40	$56.40
Purchase #7	$48.82	7.527%	$52.4947	$52.49	$52.50	$52.50
7 purchase totals =	$897.64		$976.3086	$976.31	$976.35	$976.40