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	$171.70	12.115%	$192.5015	$192.50	$192.50	$192.50
Purchase #2	$175.93	11.526%	$196.2077	$196.21	$196.20	$196.20
Purchase #3	$46.79	9.675%	$51.3169	$51.32	$51.30	$51.30
Purchase #4	$84.59	7.120%	$90.6128	$90.61	$90.60	$90.60
Purchase #5	$88.61	13.585%	$100.6477	$100.65	$100.65	$100.60
Purchase #6	$109.84	7.155%	$117.6991	$117.70	$117.70	$117.70
Purchase #7	$88.94	5.575%	$93.8984	$93.90	$93.90	$93.90
7 purchase totals =	$766.40		$842.8841	$842.89	$842.85	$842.80