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	$115.73	13.781%	$131.6788	$131.68	$131.70	$131.70
Purchase #2	$133.45	10.769%	$147.8212	$147.82	$147.80	$147.80
Purchase #3	$38.79	10.405%	$42.8261	$42.83	$42.85	$42.80
Purchase #4	$84.75	9.482%	$92.786	$92.79	$92.80	$92.80
Purchase #5	$45.48	4.132%	$47.3592	$47.36	$47.35	$47.40
Purchase #6	$132.96	7.232%	$142.5757	$142.58	$142.60	$142.60
Purchase #7	$78.91	12.599%	$88.8519	$88.85	$88.85	$88.90
7 purchase totals =	$630.07		$693.8989	$693.91	$693.95	$694.00