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	$27.26	5.425%	$28.7389	$28.74	$28.75	$28.70
Purchase #2	$50.91	7.837%	$54.8998	$54.90	$54.90	$54.90
Purchase #3	$28.88	3.407%	$29.8639	$29.86	$29.85	$29.90
Purchase #4	$235.30	9.751%	$258.2441	$258.24	$258.25	$258.20
Purchase #5	$82.46	4.633%	$86.2804	$86.28	$86.30	$86.30
Purchase #6	$28.87	10.183%	$31.8098	$31.81	$31.80	$31.80
Purchase #7	$81.35	11.318%	$90.5572	$90.56	$90.55	$90.60
7 purchase totals =	$535.03		$580.3941	$580.39	$580.40	$580.40