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	$57.89	3.699%	$60.0314	$60.03	$60.05	$60.00
Purchase #2	$222.78	10.265%	$245.6484	$245.65	$245.65	$245.60
Purchase #3	$181.83	13.470%	$206.3225	$206.32	$206.30	$206.30
Purchase #4	$64.46	11.121%	$71.6286	$71.63	$71.65	$71.60
Purchase #5	$52.66	12.749%	$59.3736	$59.37	$59.35	$59.40
Purchase #6	$36.59	7.251%	$39.2431	$39.24	$39.25	$39.20
Purchase #7	$24.95	9.118%	$27.2249	$27.22	$27.20	$27.20
7 purchase totals =	$641.16		$709.4725	$709.46	$709.45	$709.30