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	$123.36	10.108%	$135.8292	$135.83	$135.85	$135.80
Purchase #2	$140.71	7.380%	$151.0944	$151.09	$151.10	$151.10
Purchase #3	$147.76	6.829%	$157.8505	$157.85	$157.85	$157.90
Purchase #4	$139.91	10.690%	$154.8664	$154.87	$154.85	$154.90
Purchase #5	$144.68	7.673%	$155.7813	$155.78	$155.80	$155.80
Purchase #6	$248.26	12.615%	$279.578	$279.58	$279.60	$279.60
Purchase #7	$57.68	3.738%	$59.8361	$59.84	$59.85	$59.80
7 purchase totals =	$1,002.36		$1,094.8359	$1,094.84	$1,094.90	$1,094.90