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	$206.90	12.316%	$232.3818	$232.38	$232.40	$232.40
Purchase #2	$114.66	6.397%	$121.9948	$121.99	$122.00	$122.00
Purchase #3	$28.80	11.573%	$32.133	$32.13	$32.15	$32.10
Purchase #4	$129.31	8.237%	$139.9613	$139.96	$139.95	$140.00
Purchase #5	$241.61	9.647%	$264.9181	$264.92	$264.90	$264.90
Purchase #6	$146.45	3.795%	$152.0078	$152.01	$152.00	$152.00
Purchase #7	$53.85	10.543%	$59.5274	$59.53	$59.55	$59.50
7 purchase totals =	$921.58		$1,002.9242	$1,002.92	$1,002.95	$1,002.90