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	$216.74	12.252%	$243.295	$243.30	$243.30	$243.30
Purchase #2	$39.86	9.331%	$43.5793	$43.58	$43.60	$43.60
Purchase #3	$126.93	6.175%	$134.7679	$134.77	$134.75	$134.80
Purchase #4	$243.33	12.326%	$273.3229	$273.32	$273.30	$273.30
Purchase #5	$43.90	5.186%	$46.1767	$46.18	$46.20	$46.20
Purchase #6	$38.99	9.215%	$42.5829	$42.58	$42.60	$42.60
Purchase #7	$136.43	5.187%	$143.5066	$143.51	$143.50	$143.50
7 purchase totals =	$846.18		$927.2313	$927.24	$927.25	$927.30