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	$53.78	10.813%	$59.5952	$59.60	$59.60	$59.60
Purchase #2	$163.44	10.271%	$180.2269	$180.23	$180.25	$180.20
Purchase #3	$183.76	7.774%	$198.0455	$198.05	$198.05	$198.00
Purchase #4	$48.79	4.161%	$50.8202	$50.82	$50.80	$50.80
Purchase #5	$40.33	8.589%	$43.7939	$43.79	$43.80	$43.80
Purchase #6	$65.77	9.194%	$71.8169	$71.82	$71.80	$71.80
Purchase #7	$203.72	3.568%	$210.9887	$210.99	$211.00	$211.00
7 purchase totals =	$759.59		$815.2873	$815.30	$815.30	$815.20