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	$245.49	7.633%	$264.2283	$264.23	$264.25	$264.20
Purchase #2	$208.52	5.288%	$219.5465	$219.55	$219.55	$219.50
Purchase #3	$147.88	3.516%	$153.0795	$153.08	$153.10	$153.10
Purchase #4	$52.92	8.558%	$57.4489	$57.45	$57.45	$57.40
Purchase #5	$8.93	13.791%	$10.1615	$10.16	$10.15	$10.20
Purchase #6	$78.26	4.790%	$82.0087	$82.01	$82.00	$82.00
Purchase #7	$49.34	7.637%	$53.1081	$53.11	$53.10	$53.10
7 purchase totals =	$791.34		$839.5815	$839.59	$839.60	$839.50