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	$28.33	11.551%	$31.6024	$31.60	$31.60	$31.60
Purchase #2	$138.72	10.874%	$153.8044	$153.80	$153.80	$153.80
Purchase #3	$190.33	13.184%	$215.4231	$215.42	$215.40	$215.40
Purchase #4	$88.61	11.663%	$98.9446	$98.94	$98.95	$98.90
Purchase #5	$140.71	3.650%	$145.8459	$145.85	$145.85	$145.80
Purchase #6	$7.64	4.181%	$7.9594	$7.96	$7.95	$8.00
Purchase #7	$134.72	8.679%	$146.4123	$146.41	$146.40	$146.40
7 purchase totals =	$729.06		$799.9921	$799.98	$799.95	$799.90