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	$104.88	4.539%	$109.6405	$109.64	$109.65	$109.60
Purchase #2	$38.32	4.609%	$40.0862	$40.09	$40.10	$40.10
Purchase #3	$112.83	7.287%	$121.0519	$121.05	$121.05	$121.10
Purchase #4	$91.94	8.448%	$99.7071	$99.71	$99.70	$99.70
Purchase #5	$121.50	13.529%	$137.9377	$137.94	$137.95	$137.90
Purchase #6	$223.91	7.598%	$240.9227	$240.92	$240.90	$240.90
Purchase #7	$187.33	12.362%	$210.4877	$210.49	$210.50	$210.50
7 purchase totals =	$880.71		$959.8338	$959.84	$959.85	$959.80