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	$170.74	9.747%	$187.382	$187.38	$187.40	$187.40
Purchase #2	$152.87	12.244%	$171.5874	$171.59	$171.60	$171.60
Purchase #3	$198.28	12.576%	$223.2157	$223.22	$223.20	$223.20
Purchase #4	$118.96	13.170%	$134.627	$134.63	$134.65	$134.60
Purchase #5	$32.29	6.530%	$34.3985	$34.40	$34.40	$34.40
Purchase #6	$123.57	8.402%	$133.9524	$133.95	$133.95	$134.00
Purchase #7	$85.54	4.242%	$89.1686	$89.17	$89.15	$89.20
7 purchase totals =	$882.25		$974.3316	$974.34	$974.35	$974.40