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	$34.57	13.268%	$39.1567	$39.16	$39.15	$39.20
Purchase #2	$161.39	6.531%	$171.9304	$171.93	$171.95	$171.90
Purchase #3	$229.38	6.322%	$243.8814	$243.88	$243.90	$243.90
Purchase #4	$87.60	13.205%	$99.1676	$99.17	$99.15	$99.20
Purchase #5	$250.86	5.374%	$264.3412	$264.34	$264.35	$264.30
Purchase #6	$213.59	3.357%	$220.7602	$220.76	$220.75	$220.80
Purchase #7	$92.58	7.431%	$99.4596	$99.46	$99.45	$99.50
7 purchase totals =	$1,069.97		$1,138.6971	$1,138.70	$1,138.70	$1,138.80