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	$98.30	6.722%	$104.9077	$104.91	$104.90	$104.90
Purchase #2	$120.66	6.348%	$128.3195	$128.32	$128.30	$128.30
Purchase #3	$35.99	12.360%	$40.4384	$40.44	$40.45	$40.40
Purchase #4	$29.35	7.705%	$31.6114	$31.61	$31.60	$31.60
Purchase #5	$101.50	9.538%	$111.1811	$111.18	$111.20	$111.20
Purchase #6	$31.76	7.102%	$34.0156	$34.02	$34.00	$34.00
Purchase #7	$79.78	8.199%	$86.3212	$86.32	$86.30	$86.30
7 purchase totals =	$497.34		$536.7949	$536.80	$536.75	$536.70