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	$18.55	12.467%	$20.8626	$20.86	$20.85	$20.90
Purchase #2	$20.66	4.615%	$21.6135	$21.61	$21.60	$21.60
Purchase #3	$89.52	11.265%	$99.6044	$99.60	$99.60	$99.60
Purchase #4	$31.51	4.483%	$32.9226	$32.92	$32.90	$32.90
Purchase #5	$201.51	12.538%	$226.7753	$226.78	$226.80	$226.80
Purchase #6	$120.83	3.232%	$124.7352	$124.74	$124.75	$124.70
Purchase #7	$78.29	6.254%	$83.1863	$83.19	$83.20	$83.20
7 purchase totals =	$560.87		$609.6999	$609.70	$609.70	$609.70