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	$19.79	3.213%	$20.4259	$20.43	$20.45	$20.40
Purchase #2	$250.37	7.552%	$269.2779	$269.28	$269.30	$269.30
Purchase #3	$123.31	3.650%	$127.8108	$127.81	$127.80	$127.80
Purchase #4	$99.77	4.838%	$104.5969	$104.60	$104.60	$104.60
Purchase #5	$158.44	3.515%	$164.0092	$164.01	$164.00	$164.00
Purchase #6	$231.35	6.108%	$245.4809	$245.48	$245.50	$245.50
Purchase #7	$96.27	5.579%	$101.6409	$101.64	$101.65	$101.60
7 purchase totals =	$979.30		$1,033.2425	$1,033.25	$1,033.30	$1,033.20