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	$76.90	6.586%	$81.9646	$81.96	$81.95	$82.00
Purchase #2	$81.48	10.663%	$90.1682	$90.17	$90.15	$90.20
Purchase #3	$236.98	13.649%	$269.3254	$269.33	$269.35	$269.30
Purchase #4	$228.57	9.786%	$250.9379	$250.94	$250.95	$250.90
Purchase #5	$33.55	5.872%	$35.5201	$35.52	$35.50	$35.50
Purchase #6	$97.85	6.383%	$104.0958	$104.10	$104.10	$104.10
Purchase #7	$55.97	11.573%	$62.4474	$62.45	$62.45	$62.40
7 purchase totals =	$811.30		$894.4594	$894.47	$894.45	$894.40