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	$18.47	10.367%	$20.3848	$20.38	$20.40	$20.40
Purchase #2	$78.87	3.632%	$81.7346	$81.73	$81.75	$81.70
Purchase #3	$116.62	9.659%	$127.8843	$127.88	$127.90	$127.90
Purchase #4	$210.52	4.582%	$220.166	$220.17	$220.15	$220.20
Purchase #5	$42.67	3.336%	$44.0935	$44.09	$44.10	$44.10
Purchase #6	$48.37	5.316%	$50.9413	$50.94	$50.95	$50.90
Purchase #7	$221.54	13.203%	$250.7899	$250.79	$250.80	$250.80
7 purchase totals =	$737.06		$795.9944	$795.98	$796.05	$796.00