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	$234.63	8.814%	$255.3103	$255.31	$255.30	$255.30
Purchase #2	$38.27	7.585%	$41.1728	$41.17	$41.15	$41.20
Purchase #3	$91.39	4.306%	$95.3253	$95.33	$95.35	$95.30
Purchase #4	$90.25	6.264%	$95.9033	$95.90	$95.90	$95.90
Purchase #5	$232.30	3.804%	$241.1367	$241.14	$241.15	$241.10
Purchase #6	$118.32	10.560%	$130.8146	$130.81	$130.80	$130.80
Purchase #7	$19.61	6.866%	$20.9564	$20.96	$20.95	$21.00
7 purchase totals =	$824.77		$880.6194	$880.62	$880.60	$880.60