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	$40.79	13.736%	$46.3929	$46.39	$46.40	$46.40
Purchase #2	$45.73	8.699%	$49.7081	$49.71	$49.70	$49.70
Purchase #3	$74.55	12.199%	$83.6444	$83.64	$83.65	$83.60
Purchase #4	$54.89	6.555%	$58.488	$58.49	$58.50	$58.50
Purchase #5	$142.35	11.870%	$159.2469	$159.25	$159.25	$159.20
Purchase #6	$144.59	13.833%	$164.5911	$164.59	$164.60	$164.60
Purchase #7	$49.29	9.443%	$53.9445	$53.94	$53.95	$53.90
7 purchase totals =	$552.19		$616.0159	$616.01	$616.05	$615.90