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	$110.88	6.350%	$117.9209	$117.92	$117.90	$117.90
Purchase #2	$96.83	10.395%	$106.8955	$106.90	$106.90	$106.90
Purchase #3	$101.98	3.222%	$105.2658	$105.27	$105.25	$105.30
Purchase #4	$110.39	11.629%	$123.2273	$123.23	$123.25	$123.20
Purchase #5	$17.45	10.782%	$19.3315	$19.33	$19.35	$19.30
Purchase #6	$152.90	6.544%	$162.9058	$162.91	$162.90	$162.90
Purchase #7	$124.82	12.466%	$140.3801	$140.38	$140.40	$140.40
7 purchase totals =	$715.25		$775.9269	$775.94	$775.95	$775.90