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	$219.35	4.397%	$228.9948	$228.99	$229.00	$229.00
Purchase #2	$249.48	7.154%	$267.3278	$267.33	$267.35	$267.30
Purchase #3	$132.58	4.853%	$139.0141	$139.01	$139.00	$139.00
Purchase #4	$53.67	10.523%	$59.3177	$59.32	$59.30	$59.30
Purchase #5	$56.61	6.505%	$60.2925	$60.29	$60.30	$60.30
Purchase #6	$196.51	10.390%	$216.9274	$216.93	$216.95	$216.90
Purchase #7	$230.31	4.410%	$240.4667	$240.47	$240.45	$240.50
7 purchase totals =	$1,138.51		$1,212.3410	$1,212.34	$1,212.35	$1,212.30