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	$38.99	9.592%	$42.7299	$42.73	$42.75	$42.70
Purchase #2	$42.69	4.441%	$44.5859	$44.59	$44.60	$44.60
Purchase #3	$162.92	13.301%	$184.59	$184.59	$184.60	$184.60
Purchase #4	$174.95	6.169%	$185.7427	$185.74	$185.75	$185.70
Purchase #5	$88.66	9.562%	$97.1377	$97.14	$97.15	$97.10
Purchase #6	$36.25	6.651%	$38.661	$38.66	$38.65	$38.70
Purchase #7	$34.89	5.714%	$36.8836	$36.88	$36.90	$36.90
7 purchase totals =	$579.35		$630.3308	$630.33	$630.40	$630.30