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	$54.54	8.852%	$59.3679	$59.37	$59.35	$59.40
Purchase #2	$125.38	7.659%	$134.9829	$134.98	$135.00	$135.00
Purchase #3	$39.56	12.638%	$44.5596	$44.56	$44.55	$44.60
Purchase #4	$42.35	7.174%	$45.3882	$45.39	$45.40	$45.40
Purchase #5	$115.97	3.248%	$119.7367	$119.74	$119.75	$119.70
Purchase #6	$61.88	6.498%	$65.901	$65.90	$65.90	$65.90
Purchase #7	$16.36	10.849%	$18.1349	$18.13	$18.15	$18.10
7 purchase totals =	$456.04		$488.0712	$488.07	$488.10	$488.10