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	$29.74	4.615%	$31.1125	$31.11	$31.10	$31.10
Purchase #2	$86.85	8.536%	$94.2635	$94.26	$94.25	$94.30
Purchase #3	$92.35	8.696%	$100.3808	$100.38	$100.40	$100.40
Purchase #4	$196.89	10.802%	$218.1581	$218.16	$218.15	$218.20
Purchase #5	$237.82	7.703%	$256.1393	$256.14	$256.15	$256.10
Purchase #6	$51.31	6.399%	$54.5933	$54.59	$54.60	$54.60
Purchase #7	$128.73	3.213%	$132.8661	$132.87	$132.85	$132.90
7 purchase totals =	$823.69		$887.5136	$887.51	$887.50	$887.60