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	$16.57	13.814%	$18.859	$18.86	$18.85	$18.90
Purchase #2	$51.32	10.850%	$56.8882	$56.89	$56.90	$56.90
Purchase #3	$154.69	9.117%	$168.7931	$168.79	$168.80	$168.80
Purchase #4	$58.66	4.636%	$61.3795	$61.38	$61.40	$61.40
Purchase #5	$101.57	11.785%	$113.54	$113.54	$113.55	$113.50
Purchase #6	$22.96	10.627%	$25.4	$25.40	$25.40	$25.40
Purchase #7	$129.51	4.124%	$134.851	$134.85	$134.85	$134.90
7 purchase totals =	$535.28		$579.7108	$579.71	$579.75	$579.80