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	$152.66	12.401%	$171.5914	$171.59	$171.60	$171.60
Purchase #2	$92.28	13.597%	$104.8273	$104.83	$104.85	$104.80
Purchase #3	$111.44	7.309%	$119.5851	$119.59	$119.60	$119.60
Purchase #4	$65.40	9.132%	$71.3723	$71.37	$71.35	$71.40
Purchase #5	$25.61	7.190%	$27.4514	$27.45	$27.45	$27.50
Purchase #6	$44.60	10.654%	$49.3517	$49.35	$49.35	$49.40
Purchase #7	$77.63	13.463%	$88.0813	$88.08	$88.10	$88.10
7 purchase totals =	$569.62		$632.2605	$632.26	$632.30	$632.40