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	$159.85	4.403%	$166.8882	$166.89	$166.90	$166.90
Purchase #2	$156.91	6.658%	$167.3571	$167.36	$167.35	$167.40
Purchase #3	$37.51	13.654%	$42.6316	$42.63	$42.65	$42.60
Purchase #4	$59.83	10.534%	$66.1325	$66.13	$66.15	$66.10
Purchase #5	$36.54	6.401%	$38.8789	$38.88	$38.90	$38.90
Purchase #6	$206.88	9.796%	$227.146	$227.15	$227.15	$227.10
Purchase #7	$22.75	12.806%	$25.6634	$25.66	$25.65	$25.70
7 purchase totals =	$680.27		$734.6977	$734.70	$734.75	$734.70