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	$44.39	13.164%	$50.2335	$50.23	$50.25	$50.20
Purchase #2	$90.85	10.478%	$100.3693	$100.37	$100.35	$100.40
Purchase #3	$25.54	13.348%	$28.9491	$28.95	$28.95	$28.90
Purchase #4	$115.94	6.517%	$123.4958	$123.50	$123.50	$123.50
Purchase #5	$65.39	6.670%	$69.7515	$69.75	$69.75	$69.80
Purchase #6	$100.78	5.556%	$106.3793	$106.38	$106.40	$106.40
Purchase #7	$44.45	4.375%	$46.3947	$46.39	$46.40	$46.40
7 purchase totals =	$487.34		$525.5732	$525.57	$525.60	$525.60