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	$235.41	7.333%	$252.6726	$252.67	$252.65	$252.70
Purchase #2	$142.85	12.563%	$160.7962	$160.80	$160.80	$160.80
Purchase #3	$38.74	9.730%	$42.5094	$42.51	$42.50	$42.50
Purchase #4	$99.27	7.667%	$106.881	$106.88	$106.90	$106.90
Purchase #5	$89.31	11.811%	$99.8584	$99.86	$99.85	$99.90
Purchase #6	$23.74	3.114%	$24.4793	$24.48	$24.50	$24.50
Purchase #7	$47.55	10.800%	$52.6854	$52.69	$52.70	$52.70
7 purchase totals =	$676.87		$739.8823	$739.89	$739.90	$740.00