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	$49.73	8.172%	$53.7939	$53.79	$53.80	$53.80
Purchase #2	$49.89	4.747%	$52.2583	$52.26	$52.25	$52.30
Purchase #3	$116.38	8.119%	$125.8289	$125.83	$125.85	$125.80
Purchase #4	$161.62	3.304%	$166.9599	$166.96	$166.95	$167.00
Purchase #5	$78.66	8.716%	$85.516	$85.52	$85.50	$85.50
Purchase #6	$248.60	6.330%	$264.3364	$264.34	$264.35	$264.30
Purchase #7	$198.34	5.635%	$209.5165	$209.52	$209.50	$209.50
7 purchase totals =	$903.22		$958.2099	$958.22	$958.20	$958.20