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	$51.36	11.865%	$57.4539	$57.45	$57.45	$57.50
Purchase #2	$78.80	13.567%	$89.4908	$89.49	$89.50	$89.50
Purchase #3	$48.48	13.117%	$54.8391	$54.84	$54.85	$54.80
Purchase #4	$12.53	7.167%	$13.428	$13.43	$13.45	$13.40
Purchase #5	$24.50	7.869%	$26.4279	$26.43	$26.45	$26.40
Purchase #6	$85.64	10.267%	$94.4327	$94.43	$94.45	$94.40
Purchase #7	$212.92	3.102%	$219.5248	$219.52	$219.50	$219.50
7 purchase totals =	$514.23		$555.5972	$555.59	$555.65	$555.50