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	$80.86	13.155%	$91.4971	$91.50	$91.50	$91.50
Purchase #2	$172.39	5.283%	$181.4974	$181.50	$181.50	$181.50
Purchase #3	$141.41	12.804%	$159.5161	$159.52	$159.50	$159.50
Purchase #4	$139.85	3.393%	$144.5951	$144.60	$144.60	$144.60
Purchase #5	$229.32	3.763%	$237.9493	$237.95	$237.95	$237.90
Purchase #6	$76.93	7.408%	$82.629	$82.63	$82.65	$82.60
Purchase #7	$242.41	9.311%	$264.9808	$264.98	$265.00	$265.00
7 purchase totals =	$1,083.17		$1,162.6648	$1,162.68	$1,162.70	$1,162.60