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	$250.60	8.521%	$271.9536	$271.95	$271.95	$272.00
Purchase #2	$209.60	4.604%	$219.25	$219.25	$219.25	$219.30
Purchase #3	$156.81	7.460%	$168.508	$168.51	$168.50	$168.50
Purchase #4	$134.37	11.780%	$150.1988	$150.20	$150.20	$150.20
Purchase #5	$69.40	3.148%	$71.5847	$71.58	$71.60	$71.60
Purchase #6	$125.37	4.618%	$131.1596	$131.16	$131.15	$131.20
Purchase #7	$243.29	13.175%	$275.3435	$275.34	$275.35	$275.30
7 purchase totals =	$1,189.44		$1,287.9982	$1,287.99	$1,288.00	$1,288.10