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	$235.85	6.174%	$250.4114	$250.41	$250.40	$250.40
Purchase #2	$196.51	4.741%	$205.8265	$205.83	$205.85	$205.80
Purchase #3	$99.69	13.327%	$112.9757	$112.98	$113.00	$113.00
Purchase #4	$5.45	6.666%	$5.8133	$5.81	$5.80	$5.80
Purchase #5	$118.72	3.786%	$123.2147	$123.21	$123.20	$123.20
Purchase #6	$126.77	13.102%	$143.3794	$143.38	$143.40	$143.40
Purchase #7	$76.64	12.607%	$86.302	$86.30	$86.30	$86.30
7 purchase totals =	$859.63		$927.9230	$927.92	$927.95	$927.90