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	$40.68	4.614%	$42.557	$42.56	$42.55	$42.60
Purchase #2	$164.79	3.439%	$170.4571	$170.46	$170.45	$170.50
Purchase #3	$161.80	4.711%	$169.4224	$169.42	$169.40	$169.40
Purchase #4	$131.87	13.622%	$149.8333	$149.83	$149.85	$149.80
Purchase #5	$153.71	7.726%	$165.5856	$165.59	$165.60	$165.60
Purchase #6	$36.82	9.655%	$40.375	$40.38	$40.40	$40.40
Purchase #7	$241.50	10.507%	$266.8744	$266.87	$266.85	$266.90
7 purchase totals =	$931.17		$1,005.1048	$1,005.11	$1,005.10	$1,005.20