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	$141.72	12.513%	$159.4534	$159.45	$159.45	$159.50
Purchase #2	$42.31	12.418%	$47.5641	$47.56	$47.55	$47.60
Purchase #3	$6.38	12.116%	$7.153	$7.15	$7.15	$7.20
Purchase #4	$51.73	4.343%	$53.9766	$53.98	$54.00	$54.00
Purchase #5	$33.51	10.680%	$37.0889	$37.09	$37.10	$37.10
Purchase #6	$236.85	11.591%	$264.3033	$264.30	$264.30	$264.30
Purchase #7	$93.37	6.727%	$99.651	$99.65	$99.65	$99.70
7 purchase totals =	$605.87		$669.1903	$669.18	$669.20	$669.40