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	$136.78	8.830%	$148.8577	$148.86	$148.85	$148.90
Purchase #2	$171.99	6.297%	$182.8202	$182.82	$182.80	$182.80
Purchase #3	$115.64	10.282%	$127.5301	$127.53	$127.55	$127.50
Purchase #4	$105.33	13.548%	$119.6001	$119.60	$119.60	$119.60
Purchase #5	$24.65	13.589%	$27.9997	$28.00	$28.00	$28.00
Purchase #6	$132.25	11.609%	$147.6029	$147.60	$147.60	$147.60
Purchase #7	$181.65	4.465%	$189.7607	$189.76	$189.75	$189.80
7 purchase totals =	$868.29		$944.1714	$944.17	$944.15	$944.20