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	$85.71	8.866%	$93.309	$93.31	$93.30	$93.30
Purchase #2	$140.46	4.588%	$146.9043	$146.90	$146.90	$146.90
Purchase #3	$14.86	7.432%	$15.9644	$15.96	$15.95	$16.00
Purchase #4	$230.55	5.632%	$243.5346	$243.53	$243.55	$243.50
Purchase #5	$128.85	6.557%	$137.2987	$137.30	$137.30	$137.30
Purchase #6	$184.74	7.240%	$198.1152	$198.12	$198.10	$198.10
Purchase #7	$74.85	4.727%	$78.3882	$78.39	$78.40	$78.40
7 purchase totals =	$860.02		$913.5144	$913.51	$913.50	$913.50