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	$50.83	5.682%	$53.7182	$53.72	$53.70	$53.70
Purchase #2	$225.27	11.373%	$250.89	$250.89	$250.90	$250.90
Purchase #3	$13.64	6.333%	$14.5038	$14.50	$14.50	$14.50
Purchase #4	$95.67	3.709%	$99.2184	$99.22	$99.20	$99.20
Purchase #5	$49.71	6.288%	$52.8358	$52.84	$52.85	$52.80
Purchase #6	$22.71	10.456%	$25.0846	$25.08	$25.10	$25.10
Purchase #7	$224.81	8.411%	$243.7188	$243.72	$243.70	$243.70
7 purchase totals =	$682.64		$739.9696	$739.97	$739.95	$739.90