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	$160.32	12.487%	$180.3392	$180.34	$180.35	$180.30
Purchase #2	$162.93	4.442%	$170.1674	$170.17	$170.15	$170.20
Purchase #3	$78.80	13.602%	$89.5184	$89.52	$89.50	$89.50
Purchase #4	$79.31	8.156%	$85.7785	$85.78	$85.80	$85.80
Purchase #5	$92.47	5.841%	$97.8712	$97.87	$97.85	$97.90
Purchase #6	$209.33	8.486%	$227.0937	$227.09	$227.10	$227.10
Purchase #7	$162.78	3.554%	$168.5652	$168.57	$168.55	$168.60
7 purchase totals =	$945.94		$1,019.3336	$1,019.34	$1,019.30	$1,019.40