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	$33.38	12.281%	$37.4794	$37.48	$37.50	$37.50
Purchase #2	$104.99	13.800%	$119.4786	$119.48	$119.50	$119.50
Purchase #3	$229.72	9.465%	$251.463	$251.46	$251.45	$251.50
Purchase #4	$144.64	11.150%	$160.7674	$160.77	$160.75	$160.80
Purchase #5	$21.47	5.484%	$22.6474	$22.65	$22.65	$22.60
Purchase #6	$172.89	13.653%	$196.4947	$196.49	$196.50	$196.50
Purchase #7	$155.69	6.829%	$166.3221	$166.32	$166.30	$166.30
7 purchase totals =	$862.78		$954.6526	$954.65	$954.65	$954.70