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	$139.46	13.450%	$158.2174	$158.22	$158.20	$158.20
Purchase #2	$124.33	12.485%	$139.8526	$139.85	$139.85	$139.90
Purchase #3	$250.65	4.345%	$261.5407	$261.54	$261.55	$261.50
Purchase #4	$43.94	3.818%	$45.6176	$45.62	$45.60	$45.60
Purchase #5	$233.36	4.524%	$243.9172	$243.92	$243.90	$243.90
Purchase #6	$158.97	8.676%	$172.7622	$172.76	$172.75	$172.80
Purchase #7	$33.87	12.158%	$37.9879	$37.99	$38.00	$38.00
7 purchase totals =	$984.58		$1,059.8956	$1,059.90	$1,059.85	$1,059.90