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	$83.55	8.245%	$90.4387	$90.44	$90.45	$90.40
Purchase #2	$64.72	12.792%	$72.999	$73.00	$73.00	$73.00
Purchase #3	$182.28	7.308%	$195.601	$195.60	$195.60	$195.60
Purchase #4	$56.41	5.611%	$59.5752	$59.58	$59.60	$59.60
Purchase #5	$109.85	6.424%	$116.9068	$116.91	$116.90	$116.90
Purchase #6	$164.62	7.806%	$177.4702	$177.47	$177.45	$177.50
Purchase #7	$132.30	5.714%	$139.8596	$139.86	$139.85	$139.90
7 purchase totals =	$793.73		$852.8505	$852.86	$852.85	$852.90