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	$19.48	12.526%	$21.9201	$21.92	$21.90	$21.90
Purchase #2	$35.37	5.216%	$37.2149	$37.21	$37.20	$37.20
Purchase #3	$32.38	6.229%	$34.397	$34.40	$34.40	$34.40
Purchase #4	$247.51	11.332%	$275.5578	$275.56	$275.55	$275.60
Purchase #5	$196.40	4.331%	$204.9061	$204.91	$204.90	$204.90
Purchase #6	$50.64	5.508%	$53.4293	$53.43	$53.45	$53.40
Purchase #7	$233.25	9.501%	$255.4111	$255.41	$255.40	$255.40
7 purchase totals =	$815.03		$882.8363	$882.84	$882.80	$882.80