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	$84.37	7.131%	$90.3864	$90.39	$90.40	$90.40
Purchase #2	$77.58	10.820%	$85.9742	$85.97	$85.95	$86.00
Purchase #3	$93.86	10.336%	$103.5614	$103.56	$103.55	$103.60
Purchase #4	$92.70	4.600%	$96.9642	$96.96	$96.95	$97.00
Purchase #5	$203.45	8.496%	$220.7351	$220.74	$220.75	$220.70
Purchase #6	$77.78	5.402%	$81.9817	$81.98	$82.00	$82.00
Purchase #7	$154.88	11.214%	$172.2482	$172.25	$172.25	$172.20
7 purchase totals =	$784.62		$851.8512	$851.85	$851.85	$851.90