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	$86.97	3.855%	$90.3227	$90.32	$90.30	$90.30
Purchase #2	$92.72	4.167%	$96.5836	$96.58	$96.60	$96.60
Purchase #3	$172.88	8.582%	$187.7166	$187.72	$187.70	$187.70
Purchase #4	$227.61	9.701%	$249.6904	$249.69	$249.70	$249.70
Purchase #5	$110.81	3.198%	$114.3537	$114.35	$114.35	$114.40
Purchase #6	$220.98	4.455%	$230.8247	$230.82	$230.80	$230.80
Purchase #7	$161.51	6.695%	$172.3231	$172.32	$172.30	$172.30
7 purchase totals =	$1,073.48		$1,141.8148	$1,141.80	$1,141.75	$1,141.80