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	$130.45	7.139%	$139.7628	$139.76	$139.75	$139.80
Purchase #2	$67.74	10.857%	$75.0945	$75.09	$75.10	$75.10
Purchase #3	$90.51	4.164%	$94.2788	$94.28	$94.30	$94.30
Purchase #4	$16.32	9.747%	$17.9107	$17.91	$17.90	$17.90
Purchase #5	$60.87	6.738%	$64.9714	$64.97	$64.95	$65.00
Purchase #6	$74.75	8.212%	$80.8885	$80.89	$80.90	$80.90
Purchase #7	$174.88	12.567%	$196.8572	$196.86	$196.85	$196.90
7 purchase totals =	$615.52		$669.7639	$669.76	$669.75	$669.90