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	$48.85	3.382%	$50.5021	$50.50	$50.50	$50.50
Purchase #2	$77.80	3.808%	$80.7626	$80.76	$80.75	$80.80
Purchase #3	$64.39	13.843%	$73.3035	$73.30	$73.30	$73.30
Purchase #4	$90.42	4.501%	$94.4898	$94.49	$94.50	$94.50
Purchase #5	$48.86	4.171%	$50.898	$50.90	$50.90	$50.90
Purchase #6	$98.49	8.520%	$106.8813	$106.88	$106.90	$106.90
Purchase #7	$102.83	9.279%	$112.3716	$112.37	$112.35	$112.40
7 purchase totals =	$531.64		$569.2089	$569.20	$569.20	$569.30