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	$116.73	9.216%	$127.4878	$127.49	$127.50	$127.50
Purchase #2	$203.77	11.677%	$227.5642	$227.56	$227.55	$227.60
Purchase #3	$77.60	5.406%	$81.7951	$81.80	$81.80	$81.80
Purchase #4	$148.62	6.434%	$158.1822	$158.18	$158.20	$158.20
Purchase #5	$31.76	6.691%	$33.8851	$33.89	$33.90	$33.90
Purchase #6	$76.25	3.533%	$78.9439	$78.94	$78.95	$78.90
Purchase #7	$73.27	13.818%	$83.3944	$83.39	$83.40	$83.40
7 purchase totals =	$728.00		$791.2527	$791.25	$791.30	$791.30