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	$173.98	3.440%	$179.9649	$179.96	$179.95	$180.00
Purchase #2	$187.55	13.478%	$212.828	$212.83	$212.85	$212.80
Purchase #3	$86.66	3.665%	$89.8361	$89.84	$89.85	$89.80
Purchase #4	$108.73	9.385%	$118.9343	$118.93	$118.95	$118.90
Purchase #5	$176.29	13.379%	$199.8758	$199.88	$199.90	$199.90
Purchase #6	$80.46	7.834%	$86.7632	$86.76	$86.75	$86.80
Purchase #7	$11.68	5.784%	$12.3556	$12.36	$12.35	$12.40
7 purchase totals =	$825.35		$900.5579	$900.56	$900.60	$900.60