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	$140.70	6.820%	$150.2957	$150.30	$150.30	$150.30
Purchase #2	$210.76	11.464%	$234.9215	$234.92	$234.90	$234.90
Purchase #3	$71.47	5.566%	$75.448	$75.45	$75.45	$75.40
Purchase #4	$74.78	10.411%	$82.5653	$82.57	$82.55	$82.60
Purchase #5	$145.77	13.193%	$165.0014	$165.00	$165.00	$165.00
Purchase #6	$209.41	8.835%	$227.9114	$227.91	$227.90	$227.90
Purchase #7	$33.45	5.600%	$35.3232	$35.32	$35.30	$35.30
7 purchase totals =	$886.34		$971.4665	$971.47	$971.40	$971.40