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	$40.54	6.283%	$43.0871	$43.09	$43.10	$43.10
Purchase #2	$117.44	4.554%	$122.7882	$122.79	$122.80	$122.80
Purchase #3	$31.45	9.868%	$34.5535	$34.55	$34.55	$34.60
Purchase #4	$42.31	3.807%	$43.9207	$43.92	$43.90	$43.90
Purchase #5	$120.76	11.395%	$134.5206	$134.52	$134.50	$134.50
Purchase #6	$133.78	13.219%	$151.4644	$151.46	$151.45	$151.50
Purchase #7	$221.39	13.627%	$251.5588	$251.56	$251.55	$251.60
7 purchase totals =	$707.67		$781.8933	$781.89	$781.85	$782.00