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	$102.86	8.515%	$111.6185	$111.62	$111.60	$111.60
Purchase #2	$238.81	12.615%	$268.9359	$268.94	$268.95	$268.90
Purchase #3	$106.63	3.636%	$110.5071	$110.51	$110.50	$110.50
Purchase #4	$13.38	8.241%	$14.4826	$14.48	$14.50	$14.50
Purchase #5	$58.54	7.428%	$62.8884	$62.89	$62.90	$62.90
Purchase #6	$133.90	6.330%	$142.3759	$142.38	$142.40	$142.40
Purchase #7	$180.75	10.284%	$199.3383	$199.34	$199.35	$199.30
7 purchase totals =	$834.87		$910.1467	$910.16	$910.20	$910.10