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	$47.97	13.305%	$54.3524	$54.35	$54.35	$54.40
Purchase #2	$70.48	11.520%	$78.5993	$78.60	$78.60	$78.60
Purchase #3	$199.68	6.822%	$213.3022	$213.30	$213.30	$213.30
Purchase #4	$191.93	8.614%	$208.4629	$208.46	$208.45	$208.50
Purchase #5	$139.71	4.741%	$146.3337	$146.33	$146.35	$146.30
Purchase #6	$9.96	12.854%	$11.2403	$11.24	$11.25	$11.20
Purchase #7	$128.87	13.166%	$145.837	$145.84	$145.85	$145.80
7 purchase totals =	$788.60		$858.1278	$858.12	$858.15	$858.10