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	$181.30	3.777%	$188.1477	$188.15	$188.15	$188.10
Purchase #2	$137.56	6.778%	$146.8838	$146.88	$146.90	$146.90
Purchase #3	$183.91	7.803%	$198.2605	$198.26	$198.25	$198.30
Purchase #4	$199.40	11.660%	$222.65	$222.65	$222.65	$222.70
Purchase #5	$238.46	11.184%	$265.1294	$265.13	$265.15	$265.10
Purchase #6	$133.69	13.367%	$151.5603	$151.56	$151.55	$151.60
Purchase #7	$173.66	6.675%	$185.2518	$185.25	$185.25	$185.30
7 purchase totals =	$1,247.98		$1,357.8835	$1,357.88	$1,357.90	$1,358.00