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	$249.75	7.482%	$268.4363	$268.44	$268.45	$268.40
Purchase #2	$42.73	10.120%	$47.0543	$47.05	$47.05	$47.10
Purchase #3	$111.83	12.359%	$125.6511	$125.65	$125.65	$125.70
Purchase #4	$13.57	11.516%	$15.1327	$15.13	$15.15	$15.10
Purchase #5	$107.67	3.472%	$111.4083	$111.41	$111.40	$111.40
Purchase #6	$192.54	8.172%	$208.2744	$208.27	$208.25	$208.30
Purchase #7	$85.84	4.151%	$89.4032	$89.40	$89.40	$89.40
7 purchase totals =	$803.93		$865.3603	$865.35	$865.35	$865.40