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	$100.61	10.753%	$111.4286	$111.43	$111.45	$111.40
Purchase #2	$194.77	11.102%	$216.3934	$216.39	$216.40	$216.40
Purchase #3	$69.37	5.825%	$73.4108	$73.41	$73.40	$73.40
Purchase #4	$177.48	4.655%	$185.7417	$185.74	$185.75	$185.70
Purchase #5	$123.97	3.652%	$128.4974	$128.50	$128.50	$128.50
Purchase #6	$46.49	10.446%	$51.3463	$51.35	$51.35	$51.30
Purchase #7	$39.65	7.125%	$42.4751	$42.48	$42.50	$42.50
7 purchase totals =	$752.34		$809.2933	$809.30	$809.35	$809.20