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	$240.71	8.259%	$260.5902	$260.59	$260.60	$260.60
Purchase #2	$184.61	12.851%	$208.3342	$208.33	$208.35	$208.30
Purchase #3	$139.67	4.776%	$146.3406	$146.34	$146.35	$146.30
Purchase #4	$67.92	6.142%	$72.0916	$72.09	$72.10	$72.10
Purchase #5	$212.57	4.728%	$222.6203	$222.62	$222.60	$222.60
Purchase #6	$97.81	11.302%	$108.8645	$108.86	$108.85	$108.90
Purchase #7	$102.32	7.278%	$109.7668	$109.77	$109.75	$109.80
7 purchase totals =	$1,045.61		$1,128.6082	$1,128.60	$1,128.60	$1,128.60