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	$75.37	13.842%	$85.8027	$85.80	$85.80	$85.80
Purchase #2	$82.76	10.630%	$91.5574	$91.56	$91.55	$91.60
Purchase #3	$167.39	9.469%	$183.2402	$183.24	$183.25	$183.20
Purchase #4	$145.28	3.436%	$150.2718	$150.27	$150.25	$150.30
Purchase #5	$145.33	9.455%	$159.071	$159.07	$159.05	$159.10
Purchase #6	$61.87	9.277%	$67.6097	$67.61	$67.60	$67.60
Purchase #7	$10.64	10.230%	$11.7285	$11.73	$11.75	$11.70
7 purchase totals =	$688.64		$749.2813	$749.28	$749.25	$749.30