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	$106.38	6.137%	$112.9085	$112.91	$112.90	$112.90
Purchase #2	$68.46	11.117%	$76.0707	$76.07	$76.05	$76.10
Purchase #3	$116.38	12.671%	$131.1265	$131.13	$131.15	$131.10
Purchase #4	$20.38	11.666%	$22.7575	$22.76	$22.75	$22.80
Purchase #5	$76.81	6.289%	$81.6406	$81.64	$81.65	$81.60
Purchase #6	$55.63	12.556%	$62.6149	$62.61	$62.60	$62.60
Purchase #7	$106.55	13.355%	$120.7798	$120.78	$120.80	$120.80
7 purchase totals =	$550.59		$607.8985	$607.90	$607.90	$607.90