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	$76.57	4.260%	$79.8319	$79.83	$79.85	$79.80
Purchase #2	$56.68	9.585%	$62.1128	$62.11	$62.10	$62.10
Purchase #3	$122.94	9.630%	$134.7791	$134.78	$134.80	$134.80
Purchase #4	$47.76	12.658%	$53.8055	$53.81	$53.80	$53.80
Purchase #5	$40.48	4.653%	$42.3635	$42.36	$42.35	$42.40
Purchase #6	$55.78	6.521%	$59.4174	$59.42	$59.40	$59.40
Purchase #7	$89.82	11.767%	$100.3891	$100.39	$100.40	$100.40
7 purchase totals =	$490.03		$532.6993	$532.70	$532.70	$532.70