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	$152.90	8.420%	$165.7742	$165.77	$165.75	$165.80
Purchase #2	$38.83	3.360%	$40.1347	$40.13	$40.15	$40.10
Purchase #3	$6.92	8.857%	$7.5329	$7.53	$7.55	$7.50
Purchase #4	$10.89	5.315%	$11.4688	$11.47	$11.45	$11.50
Purchase #5	$26.91	3.705%	$27.907	$27.91	$27.90	$27.90
Purchase #6	$224.74	7.188%	$240.8943	$240.89	$240.90	$240.90
Purchase #7	$197.28	13.266%	$223.4512	$223.45	$223.45	$223.50
7 purchase totals =	$658.47		$717.1631	$717.15	$717.15	$717.20