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	$51.48	6.288%	$54.7171	$54.72	$54.70	$54.70
Purchase #2	$88.72	12.554%	$99.8579	$99.86	$99.85	$99.90
Purchase #3	$148.57	12.654%	$167.37	$167.37	$167.35	$167.40
Purchase #4	$59.36	9.728%	$65.1345	$65.13	$65.15	$65.10
Purchase #5	$83.60	3.435%	$86.4717	$86.47	$86.45	$86.50
Purchase #6	$16.57	9.707%	$18.1784	$18.18	$18.20	$18.20
Purchase #7	$165.35	7.395%	$177.5776	$177.58	$177.60	$177.60
7 purchase totals =	$613.65		$669.3072	$669.31	$669.30	$669.40