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	$177.35	6.210%	$188.3634	$188.36	$188.35	$188.40
Purchase #2	$71.58	7.480%	$76.9342	$76.93	$76.95	$76.90
Purchase #3	$118.81	10.437%	$131.2102	$131.21	$131.20	$131.20
Purchase #4	$38.91	9.219%	$42.4971	$42.50	$42.50	$42.50
Purchase #5	$32.74	3.185%	$33.7828	$33.78	$33.80	$33.80
Purchase #6	$40.74	8.285%	$44.1153	$44.12	$44.10	$44.10
Purchase #7	$152.89	6.184%	$162.3447	$162.34	$162.35	$162.30
7 purchase totals =	$633.02		$679.2477	$679.24	$679.25	$679.20