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	$6.78	8.811%	$7.3774	$7.38	$7.40	$7.40
Purchase #2	$78.85	8.846%	$85.8251	$85.83	$85.85	$85.80
Purchase #3	$193.87	12.203%	$217.528	$217.53	$217.55	$217.50
Purchase #4	$112.52	10.198%	$123.9948	$123.99	$124.00	$124.00
Purchase #5	$55.78	5.860%	$59.0487	$59.05	$59.05	$59.00
Purchase #6	$19.85	11.425%	$22.1179	$22.12	$22.10	$22.10
Purchase #7	$90.72	5.205%	$95.442	$95.44	$95.45	$95.40
7 purchase totals =	$558.37		$611.3339	$611.34	$611.40	$611.20