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	$25.89	10.140%	$28.5152	$28.52	$28.50	$28.50
Purchase #2	$215.94	11.272%	$240.2808	$240.28	$240.30	$240.30
Purchase #3	$32.62	4.596%	$34.1192	$34.12	$34.10	$34.10
Purchase #4	$131.85	10.515%	$145.714	$145.71	$145.70	$145.70
Purchase #5	$145.41	3.154%	$149.9962	$150.00	$150.00	$150.00
Purchase #6	$82.67	3.295%	$85.394	$85.39	$85.40	$85.40
Purchase #7	$54.66	7.757%	$58.9	$58.90	$58.90	$58.90
7 purchase totals =	$689.04		$742.9194	$742.92	$742.90	$742.90