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	$169.86	6.550%	$180.9858	$180.99	$181.00	$181.00
Purchase #2	$146.90	8.177%	$158.912	$158.91	$158.90	$158.90
Purchase #3	$237.39	4.217%	$247.4007	$247.40	$247.40	$247.40
Purchase #4	$90.38	10.413%	$99.7913	$99.79	$99.80	$99.80
Purchase #5	$95.51	9.276%	$104.3695	$104.37	$104.35	$104.40
Purchase #6	$155.76	3.291%	$160.8861	$160.89	$160.90	$160.90
Purchase #7	$94.55	5.281%	$99.5432	$99.54	$99.55	$99.50
7 purchase totals =	$990.35		$1,051.8886	$1,051.89	$1,051.90	$1,051.90