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	$45.97	13.507%	$52.1792	$52.18	$52.20	$52.20
Purchase #2	$32.76	3.230%	$33.8181	$33.82	$33.80	$33.80
Purchase #3	$55.31	7.331%	$59.3648	$59.36	$59.35	$59.40
Purchase #4	$234.39	8.856%	$255.1476	$255.15	$255.15	$255.10
Purchase #5	$49.89	9.768%	$54.7633	$54.76	$54.75	$54.80
Purchase #6	$77.88	3.516%	$80.6183	$80.62	$80.60	$80.60
Purchase #7	$233.28	9.570%	$255.6049	$255.60	$255.60	$255.60
7 purchase totals =	$729.48		$791.4962	$791.49	$791.45	$791.50