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	$220.51	12.249%	$247.5203	$247.52	$247.50	$247.50
Purchase #2	$131.88	13.774%	$150.0452	$150.05	$150.05	$150.00
Purchase #3	$246.68	11.495%	$275.0359	$275.04	$275.05	$275.00
Purchase #4	$82.44	5.411%	$86.9008	$86.90	$86.90	$86.90
Purchase #5	$216.32	6.847%	$231.1314	$231.13	$231.15	$231.10
Purchase #6	$79.75	7.107%	$85.4178	$85.42	$85.40	$85.40
Purchase #7	$11.99	9.310%	$13.1063	$13.11	$13.10	$13.10
7 purchase totals =	$989.57		$1,089.1577	$1,089.17	$1,089.15	$1,089.00