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	$12.33	4.529%	$12.8884	$12.89	$12.90	$12.90
Purchase #2	$149.27	11.392%	$166.2748	$166.27	$166.25	$166.30
Purchase #3	$76.66	12.751%	$86.4349	$86.43	$86.45	$86.40
Purchase #4	$57.31	6.869%	$61.2466	$61.25	$61.25	$61.20
Purchase #5	$131.73	11.693%	$147.1332	$147.13	$147.15	$147.10
Purchase #6	$248.37	12.508%	$279.4361	$279.44	$279.45	$279.40
Purchase #7	$153.38	4.293%	$159.9646	$159.96	$159.95	$160.00
7 purchase totals =	$829.05		$913.3786	$913.37	$913.40	$913.30