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	$10.48	4.124%	$10.9122	$10.91	$10.90	$10.90
Purchase #2	$158.88	9.237%	$173.5557	$173.56	$173.55	$173.60
Purchase #3	$162.73	10.388%	$179.6344	$179.63	$179.65	$179.60
Purchase #4	$73.56	3.853%	$76.3943	$76.39	$76.40	$76.40
Purchase #5	$81.74	10.282%	$90.1445	$90.14	$90.15	$90.10
Purchase #6	$81.60	6.405%	$86.8265	$86.83	$86.85	$86.80
Purchase #7	$119.46	10.129%	$131.5601	$131.56	$131.55	$131.60
7 purchase totals =	$688.45		$749.0277	$749.02	$749.05	$749.00