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	$29.56	5.864%	$31.2934	$31.29	$31.30	$31.30
Purchase #2	$54.43	3.352%	$56.2545	$56.25	$56.25	$56.30
Purchase #3	$18.50	4.268%	$19.2896	$19.29	$19.30	$19.30
Purchase #4	$166.65	7.786%	$179.6254	$179.63	$179.65	$179.60
Purchase #5	$94.74	6.493%	$100.8915	$100.89	$100.90	$100.90
Purchase #6	$223.56	6.218%	$237.461	$237.46	$237.45	$237.50
Purchase #7	$186.35	13.405%	$211.3302	$211.33	$211.35	$211.30
7 purchase totals =	$773.79		$836.1456	$836.14	$836.20	$836.20