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	$23.27	8.740%	$25.3038	$25.30	$25.30	$25.30
Purchase #2	$29.54	9.107%	$32.2302	$32.23	$32.25	$32.20
Purchase #3	$176.46	12.788%	$199.0257	$199.03	$199.05	$199.00
Purchase #4	$7.94	11.554%	$8.8574	$8.86	$8.85	$8.90
Purchase #5	$59.62	10.351%	$65.7913	$65.79	$65.80	$65.80
Purchase #6	$95.71	4.383%	$99.905	$99.91	$99.90	$99.90
Purchase #7	$149.88	7.297%	$160.8167	$160.82	$160.80	$160.80
7 purchase totals =	$542.42		$591.9301	$591.94	$591.95	$591.90