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	$51.38	13.340%	$58.2341	$58.23	$58.25	$58.20
Purchase #2	$87.63	10.429%	$96.7689	$96.77	$96.75	$96.80
Purchase #3	$165.47	10.538%	$182.9072	$182.91	$182.90	$182.90
Purchase #4	$87.39	13.739%	$99.3965	$99.40	$99.40	$99.40
Purchase #5	$93.42	7.866%	$100.7684	$100.77	$100.75	$100.80
Purchase #6	$115.63	12.310%	$129.8641	$129.86	$129.85	$129.90
Purchase #7	$151.60	10.557%	$167.6044	$167.60	$167.60	$167.60
7 purchase totals =	$752.52		$835.5436	$835.54	$835.50	$835.60