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	$47.38	8.740%	$51.521	$51.52	$51.50	$51.50
Purchase #2	$212.81	5.421%	$224.3464	$224.35	$224.35	$224.30
Purchase #3	$115.69	10.115%	$127.392	$127.39	$127.40	$127.40
Purchase #4	$130.89	9.135%	$142.8468	$142.85	$142.85	$142.80
Purchase #5	$211.93	6.114%	$224.8874	$224.89	$224.90	$224.90
Purchase #6	$178.68	4.654%	$186.9958	$187.00	$187.00	$187.00
Purchase #7	$216.99	11.274%	$241.4535	$241.45	$241.45	$241.50
7 purchase totals =	$1,114.37		$1,199.4429	$1,199.45	$1,199.45	$1,199.40