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	$238.73	4.725%	$250.01	$250.01	$250.00	$250.00
Purchase #2	$31.61	7.272%	$33.9087	$33.91	$33.90	$33.90
Purchase #3	$214.66	13.604%	$243.8623	$243.86	$243.85	$243.90
Purchase #4	$19.46	10.586%	$21.52	$21.52	$21.50	$21.50
Purchase #5	$28.51	5.789%	$30.1604	$30.16	$30.15	$30.20
Purchase #6	$96.78	6.622%	$103.1888	$103.19	$103.20	$103.20
Purchase #7	$84.49	8.742%	$91.8761	$91.88	$91.90	$91.90
7 purchase totals =	$714.24		$774.5263	$774.53	$774.50	$774.60