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	$161.53	4.254%	$168.4015	$168.40	$168.40	$168.40
Purchase #2	$77.53	6.151%	$82.2989	$82.30	$82.30	$82.30
Purchase #3	$99.83	4.367%	$104.1896	$104.19	$104.20	$104.20
Purchase #4	$84.59	9.499%	$92.6252	$92.63	$92.65	$92.60
Purchase #5	$134.42	3.596%	$139.2537	$139.25	$139.25	$139.30
Purchase #6	$161.49	3.612%	$167.323	$167.32	$167.30	$167.30
Purchase #7	$84.84	7.771%	$91.4329	$91.43	$91.45	$91.40
7 purchase totals =	$804.23		$845.5248	$845.52	$845.55	$845.50