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	$104.93	6.117%	$111.3486	$111.35	$111.35	$111.30
Purchase #2	$119.95	6.287%	$127.4913	$127.49	$127.50	$127.50
Purchase #3	$123.62	13.129%	$139.8501	$139.85	$139.85	$139.90
Purchase #4	$86.63	8.352%	$93.8653	$93.87	$93.85	$93.90
Purchase #5	$25.46	10.307%	$28.0842	$28.08	$28.10	$28.10
Purchase #6	$226.76	8.168%	$245.2818	$245.28	$245.30	$245.30
Purchase #7	$219.79	12.386%	$247.0132	$247.01	$247.00	$247.00
7 purchase totals =	$907.14		$992.9345	$992.93	$992.95	$993.00