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	$159.90	12.299%	$179.5661	$179.57	$179.55	$179.60
Purchase #2	$213.66	4.470%	$223.2106	$223.21	$223.20	$223.20
Purchase #3	$35.51	10.814%	$39.3501	$39.35	$39.35	$39.40
Purchase #4	$104.73	12.755%	$118.0883	$118.09	$118.10	$118.10
Purchase #5	$12.30	7.420%	$13.2127	$13.21	$13.20	$13.20
Purchase #6	$57.59	3.556%	$59.6379	$59.64	$59.65	$59.60
Purchase #7	$223.63	4.677%	$234.0892	$234.09	$234.10	$234.10
7 purchase totals =	$807.32		$867.1549	$867.16	$867.15	$867.20