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	$173.27	8.369%	$187.771	$187.77	$187.75	$187.80
Purchase #2	$83.41	7.195%	$89.4113	$89.41	$89.40	$89.40
Purchase #3	$46.97	3.616%	$48.6684	$48.67	$48.65	$48.70
Purchase #4	$32.95	3.255%	$34.0225	$34.02	$34.00	$34.00
Purchase #5	$137.65	7.414%	$147.8554	$147.86	$147.85	$147.90
Purchase #6	$55.55	12.556%	$62.5249	$62.52	$62.50	$62.50
Purchase #7	$81.61	11.250%	$90.7911	$90.79	$90.80	$90.80
7 purchase totals =	$611.41		$661.0446	$661.04	$660.95	$661.10