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	$6.36	12.635%	$7.1636	$7.16	$7.15	$7.20
Purchase #2	$39.98	11.154%	$44.4394	$44.44	$44.45	$44.40
Purchase #3	$181.45	3.855%	$188.4449	$188.44	$188.45	$188.40
Purchase #4	$157.56	4.759%	$165.0583	$165.06	$165.05	$165.10
Purchase #5	$105.79	7.480%	$113.7031	$113.70	$113.70	$113.70
Purchase #6	$114.90	10.577%	$127.053	$127.05	$127.05	$127.10
Purchase #7	$87.56	5.645%	$92.5028	$92.50	$92.50	$92.50
7 purchase totals =	$693.60		$738.3651	$738.35	$738.35	$738.40