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	$150.56	11.357%	$167.6591	$167.66	$167.65	$167.70
Purchase #2	$233.49	7.760%	$251.6088	$251.61	$251.60	$251.60
Purchase #3	$99.94	4.568%	$104.5053	$104.51	$104.50	$104.50
Purchase #4	$11.73	3.229%	$12.1088	$12.11	$12.10	$12.10
Purchase #5	$179.96	11.419%	$200.5096	$200.51	$200.50	$200.50
Purchase #6	$72.36	7.318%	$77.6553	$77.66	$77.65	$77.70
Purchase #7	$81.54	5.341%	$85.8951	$85.90	$85.90	$85.90
7 purchase totals =	$829.58		$899.9420	$899.96	$899.90	$900.00