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	$35.34	12.428%	$39.7321	$39.73	$39.75	$39.70
Purchase #2	$144.72	10.723%	$160.2383	$160.24	$160.25	$160.20
Purchase #3	$186.83	4.659%	$195.5344	$195.53	$195.55	$195.50
Purchase #4	$138.44	9.204%	$151.182	$151.18	$151.20	$151.20
Purchase #5	$205.26	7.288%	$220.2193	$220.22	$220.20	$220.20
Purchase #6	$96.44	4.171%	$100.4625	$100.46	$100.45	$100.50
Purchase #7	$72.42	13.848%	$82.4487	$82.45	$82.45	$82.40
7 purchase totals =	$879.45		$949.8173	$949.81	$949.85	$949.70