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	$100.58	12.520%	$113.1726	$113.17	$113.15	$113.20
Purchase #2	$90.52	7.568%	$97.3706	$97.37	$97.35	$97.40
Purchase #3	$28.54	9.518%	$31.2564	$31.26	$31.25	$31.30
Purchase #4	$31.65	6.747%	$33.7854	$33.79	$33.80	$33.80
Purchase #5	$170.55	12.247%	$191.4373	$191.44	$191.45	$191.40
Purchase #6	$78.87	13.650%	$89.6358	$89.64	$89.65	$89.60
Purchase #7	$244.92	8.582%	$265.939	$265.94	$265.95	$265.90
7 purchase totals =	$745.63		$822.5971	$822.61	$822.60	$822.60