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	$120.26	7.660%	$129.4719	$129.47	$129.45	$129.50
Purchase #2	$222.53	3.288%	$229.8468	$229.85	$229.85	$229.80
Purchase #3	$171.39	8.495%	$185.9496	$185.95	$185.95	$185.90
Purchase #4	$38.30	9.587%	$41.9718	$41.97	$41.95	$42.00
Purchase #5	$108.35	7.654%	$116.6431	$116.64	$116.65	$116.60
Purchase #6	$98.51	13.191%	$111.5045	$111.50	$111.50	$111.50
Purchase #7	$78.58	3.661%	$81.4568	$81.46	$81.45	$81.50
7 purchase totals =	$837.92		$896.8445	$896.84	$896.80	$896.80