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	$47.89	8.366%	$51.8965	$51.90	$51.90	$51.90
Purchase #2	$33.92	10.327%	$37.4229	$37.42	$37.40	$37.40
Purchase #3	$137.81	13.238%	$156.0533	$156.05	$156.05	$156.10
Purchase #4	$218.93	11.441%	$243.9778	$243.98	$244.00	$244.00
Purchase #5	$183.77	7.168%	$196.9426	$196.94	$196.95	$196.90
Purchase #6	$153.28	10.515%	$169.3974	$169.40	$169.40	$169.40
Purchase #7	$85.37	6.148%	$90.6185	$90.62	$90.60	$90.60
7 purchase totals =	$860.97		$946.3090	$946.31	$946.30	$946.30