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	$108.66	4.425%	$113.4682	$113.47	$113.45	$113.50
Purchase #2	$98.46	12.787%	$111.0501	$111.05	$111.05	$111.10
Purchase #3	$123.83	12.603%	$139.4363	$139.44	$139.45	$139.40
Purchase #4	$91.88	11.271%	$102.2358	$102.24	$102.25	$102.20
Purchase #5	$75.80	8.449%	$82.2043	$82.20	$82.20	$82.20
Purchase #6	$248.52	6.774%	$265.3547	$265.35	$265.35	$265.40
Purchase #7	$57.85	11.552%	$64.5328	$64.53	$64.55	$64.50
7 purchase totals =	$805.00		$878.2822	$878.28	$878.30	$878.30