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	$76.33	5.447%	$80.4877	$80.49	$80.50	$80.50
Purchase #2	$218.95	12.223%	$245.7123	$245.71	$245.70	$245.70
Purchase #3	$29.77	6.608%	$31.7372	$31.74	$31.75	$31.70
Purchase #4	$82.88	11.637%	$92.5247	$92.52	$92.50	$92.50
Purchase #5	$164.42	12.313%	$184.665	$184.67	$184.65	$184.70
Purchase #6	$81.69	12.123%	$91.5933	$91.59	$91.60	$91.60
Purchase #7	$192.82	12.466%	$216.8569	$216.86	$216.85	$216.90
7 purchase totals =	$846.86		$943.5771	$943.58	$943.55	$943.60