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	$74.49	11.827%	$83.2999	$83.30	$83.30	$83.30
Purchase #2	$51.92	7.819%	$55.9796	$55.98	$56.00	$56.00
Purchase #3	$100.47	8.524%	$109.0341	$109.03	$109.05	$109.00
Purchase #4	$54.27	8.377%	$58.8162	$58.82	$58.80	$58.80
Purchase #5	$215.57	11.267%	$239.8583	$239.86	$239.85	$239.90
Purchase #6	$118.59	11.309%	$132.0013	$132.00	$132.00	$132.00
Purchase #7	$55.28	7.413%	$59.3779	$59.38	$59.40	$59.40
7 purchase totals =	$670.59		$738.3673	$738.37	$738.40	$738.40