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	$16.88	8.384%	$18.2952	$18.30	$18.30	$18.30
Purchase #2	$38.41	3.680%	$39.8235	$39.82	$39.80	$39.80
Purchase #3	$182.36	7.685%	$196.3744	$196.37	$196.35	$196.40
Purchase #4	$221.63	5.638%	$234.1255	$234.13	$234.15	$234.10
Purchase #5	$36.72	7.136%	$39.3403	$39.34	$39.35	$39.30
Purchase #6	$167.44	13.717%	$190.4077	$190.41	$190.40	$190.40
Purchase #7	$72.99	10.628%	$80.7474	$80.75	$80.75	$80.70
7 purchase totals =	$736.43		$799.1140	$799.12	$799.10	$799.00