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	$76.77	4.391%	$80.141	$80.14	$80.15	$80.10
Purchase #2	$53.96	5.602%	$56.9828	$56.98	$57.00	$57.00
Purchase #3	$77.44	12.221%	$86.9039	$86.90	$86.90	$86.90
Purchase #4	$210.74	7.798%	$227.1735	$227.17	$227.15	$227.20
Purchase #5	$37.65	11.160%	$41.8517	$41.85	$41.85	$41.90
Purchase #6	$146.55	10.760%	$162.3188	$162.32	$162.30	$162.30
Purchase #7	$112.61	13.645%	$127.9756	$127.98	$128.00	$128.00
7 purchase totals =	$715.72		$783.3473	$783.34	$783.35	$783.40