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	$131.27	4.257%	$136.8582	$136.86	$136.85	$136.90
Purchase #2	$239.28	10.667%	$264.804	$264.80	$264.80	$264.80
Purchase #3	$50.78	11.726%	$56.7345	$56.73	$56.75	$56.70
Purchase #4	$162.33	3.696%	$168.3297	$168.33	$168.35	$168.30
Purchase #5	$132.56	3.755%	$137.5376	$137.54	$137.55	$137.50
Purchase #6	$72.46	6.573%	$77.2228	$77.22	$77.20	$77.20
Purchase #7	$123.45	5.800%	$130.6101	$130.61	$130.60	$130.60
7 purchase totals =	$912.13		$972.0969	$972.09	$972.10	$972.00