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	$26.71	13.354%	$30.2769	$30.28	$30.30	$30.30
Purchase #2	$132.83	8.183%	$143.6995	$143.70	$143.70	$143.70
Purchase #3	$159.34	9.504%	$174.4837	$174.48	$174.50	$174.50
Purchase #4	$96.71	6.607%	$103.0996	$103.10	$103.10	$103.10
Purchase #5	$210.98	6.421%	$224.527	$224.53	$224.55	$224.50
Purchase #6	$237.69	5.346%	$250.3969	$250.40	$250.40	$250.40
Purchase #7	$118.32	4.290%	$123.3959	$123.40	$123.40	$123.40
7 purchase totals =	$982.58		$1,049.8795	$1,049.89	$1,049.95	$1,049.90