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	$63.42	12.681%	$71.4623	$71.46	$71.45	$71.50
Purchase #2	$178.65	9.408%	$195.4574	$195.46	$195.45	$195.50
Purchase #3	$205.89	11.136%	$228.8179	$228.82	$228.80	$228.80
Purchase #4	$19.46	13.544%	$22.0957	$22.10	$22.10	$22.10
Purchase #5	$170.77	9.438%	$186.8873	$186.89	$186.90	$186.90
Purchase #6	$21.51	9.541%	$23.5623	$23.56	$23.55	$23.60
Purchase #7	$75.65	3.800%	$78.5247	$78.52	$78.50	$78.50
7 purchase totals =	$735.35		$806.8076	$806.81	$806.75	$806.90