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	$86.43	3.406%	$89.3738	$89.37	$89.35	$89.40
Purchase #2	$73.49	12.784%	$82.885	$82.89	$82.90	$82.90
Purchase #3	$45.62	13.691%	$51.8658	$51.87	$51.85	$51.90
Purchase #4	$84.61	6.814%	$90.3753	$90.38	$90.40	$90.40
Purchase #5	$102.73	4.262%	$107.1084	$107.11	$107.10	$107.10
Purchase #6	$36.92	13.541%	$41.9193	$41.92	$41.90	$41.90
Purchase #7	$25.87	9.617%	$28.3579	$28.36	$28.35	$28.40
7 purchase totals =	$455.67		$491.8855	$491.90	$491.85	$492.00