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	$69.34	3.154%	$71.527	$71.53	$71.55	$71.50
Purchase #2	$124.37	13.365%	$140.9921	$140.99	$141.00	$141.00
Purchase #3	$125.51	7.353%	$134.7388	$134.74	$134.75	$134.70
Purchase #4	$19.83	6.840%	$21.1864	$21.19	$21.20	$21.20
Purchase #5	$82.94	8.741%	$90.1898	$90.19	$90.20	$90.20
Purchase #6	$103.86	5.523%	$109.5962	$109.60	$109.60	$109.60
Purchase #7	$194.65	13.696%	$221.3093	$221.31	$221.30	$221.30
7 purchase totals =	$720.50		$789.5396	$789.55	$789.60	$789.50