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	$50.63	6.301%	$53.8202	$53.82	$53.80	$53.80
Purchase #2	$5.60	4.558%	$5.8552	$5.86	$5.85	$5.90
Purchase #3	$145.29	11.748%	$162.3587	$162.36	$162.35	$162.40
Purchase #4	$43.47	4.272%	$45.327	$45.33	$45.35	$45.30
Purchase #5	$22.56	9.845%	$24.781	$24.78	$24.80	$24.80
Purchase #6	$96.47	7.574%	$103.7766	$103.78	$103.80	$103.80
Purchase #7	$95.85	9.270%	$104.7353	$104.74	$104.75	$104.70
7 purchase totals =	$459.87		$500.6540	$500.67	$500.70	$500.70