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	$127.73	10.265%	$140.8415	$140.84	$140.85	$140.80
Purchase #2	$54.41	6.144%	$57.753	$57.75	$57.75	$57.80
Purchase #3	$148.54	4.236%	$154.8322	$154.83	$154.85	$154.80
Purchase #4	$236.76	3.360%	$244.7151	$244.72	$244.70	$244.70
Purchase #5	$16.61	13.542%	$18.8593	$18.86	$18.85	$18.90
Purchase #6	$179.94	5.766%	$190.3153	$190.32	$190.30	$190.30
Purchase #7	$90.60	9.850%	$99.5241	$99.52	$99.50	$99.50
7 purchase totals =	$854.59		$906.8405	$906.84	$906.80	$906.80