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	$81.99	7.140%	$87.8441	$87.84	$87.85	$87.80
Purchase #2	$134.83	11.237%	$149.9808	$149.98	$150.00	$150.00
Purchase #3	$51.66	6.297%	$54.913	$54.91	$54.90	$54.90
Purchase #4	$175.76	12.700%	$198.0815	$198.08	$198.10	$198.10
Purchase #5	$116.30	12.854%	$131.2492	$131.25	$131.25	$131.20
Purchase #6	$67.59	6.439%	$71.9421	$71.94	$71.95	$71.90
Purchase #7	$18.65	13.773%	$21.2187	$21.22	$21.20	$21.20
7 purchase totals =	$646.78		$715.2294	$715.22	$715.25	$715.10