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	$163.44	4.704%	$171.1282	$171.13	$171.15	$171.10
Purchase #2	$161.82	4.349%	$168.8576	$168.86	$168.85	$168.90
Purchase #3	$67.99	10.183%	$74.9134	$74.91	$74.90	$74.90
Purchase #4	$38.90	4.512%	$40.6552	$40.66	$40.65	$40.70
Purchase #5	$128.41	8.248%	$139.0013	$139.00	$139.00	$139.00
Purchase #6	$31.32	4.670%	$32.7826	$32.78	$32.80	$32.80
Purchase #7	$92.81	12.185%	$104.1189	$104.12	$104.10	$104.10
7 purchase totals =	$684.69		$731.4572	$731.46	$731.45	$731.50