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	$74.82	5.301%	$78.7862	$78.79	$78.80	$78.80
Purchase #2	$199.60	10.812%	$221.1808	$221.18	$221.20	$221.20
Purchase #3	$91.33	10.210%	$100.6548	$100.65	$100.65	$100.70
Purchase #4	$168.38	4.555%	$176.0497	$176.05	$176.05	$176.00
Purchase #5	$174.85	3.425%	$180.8386	$180.84	$180.85	$180.80
Purchase #6	$249.82	9.633%	$273.8852	$273.89	$273.90	$273.90
Purchase #7	$10.63	3.611%	$11.0138	$11.01	$11.00	$11.00
7 purchase totals =	$969.43		$1,042.4091	$1,042.41	$1,042.45	$1,042.40