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	$72.35	13.871%	$82.3857	$82.39	$82.40	$82.40
Purchase #2	$129.38	3.629%	$134.0752	$134.08	$134.10	$134.10
Purchase #3	$9.99	3.411%	$10.3308	$10.33	$10.35	$10.30
Purchase #4	$139.64	9.485%	$152.8849	$152.88	$152.90	$152.90
Purchase #5	$129.27	13.148%	$146.2664	$146.27	$146.25	$146.30
Purchase #6	$13.26	13.301%	$15.0237	$15.02	$15.00	$15.00
Purchase #7	$126.64	3.859%	$131.527	$131.53	$131.55	$131.50
7 purchase totals =	$620.53		$672.4937	$672.50	$672.55	$672.50