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	$221.32	3.844%	$229.8275	$229.83	$229.85	$229.80
Purchase #2	$155.72	8.789%	$169.4062	$169.41	$169.40	$169.40
Purchase #3	$40.93	4.239%	$42.665	$42.67	$42.65	$42.70
Purchase #4	$160.67	12.436%	$180.6509	$180.65	$180.65	$180.70
Purchase #5	$154.54	3.457%	$159.8824	$159.88	$159.90	$159.90
Purchase #6	$59.50	8.418%	$64.5087	$64.51	$64.50	$64.50
Purchase #7	$83.35	9.520%	$91.2849	$91.28	$91.30	$91.30
7 purchase totals =	$876.03		$938.2256	$938.23	$938.25	$938.30