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	$189.51	3.636%	$196.4006	$196.40	$196.40	$196.40
Purchase #2	$203.42	12.195%	$228.2271	$228.23	$228.25	$228.20
Purchase #3	$86.25	7.116%	$92.3876	$92.39	$92.40	$92.40
Purchase #4	$146.95	4.368%	$153.3688	$153.37	$153.35	$153.40
Purchase #5	$45.53	13.136%	$51.5108	$51.51	$51.50	$51.50
Purchase #6	$28.45	11.804%	$31.8082	$31.81	$31.80	$31.80
Purchase #7	$45.42	10.501%	$50.1896	$50.19	$50.20	$50.20
7 purchase totals =	$745.53		$803.8927	$803.90	$803.90	$803.90