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	$13.59	12.519%	$15.2913	$15.29	$15.30	$15.30
Purchase #2	$201.66	4.600%	$210.9364	$210.94	$210.95	$210.90
Purchase #3	$38.59	10.775%	$42.7481	$42.75	$42.75	$42.70
Purchase #4	$83.90	7.776%	$90.4241	$90.42	$90.40	$90.40
Purchase #5	$36.52	9.840%	$40.1136	$40.11	$40.10	$40.10
Purchase #6	$143.84	4.270%	$149.982	$149.98	$150.00	$150.00
Purchase #7	$145.48	13.230%	$164.727	$164.73	$164.75	$164.70
7 purchase totals =	$663.58		$714.2225	$714.22	$714.25	$714.10