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	$172.83	9.313%	$188.9257	$188.93	$188.95	$188.90
Purchase #2	$133.67	6.591%	$142.4802	$142.48	$142.50	$142.50
Purchase #3	$154.61	9.632%	$169.502	$169.50	$169.50	$169.50
Purchase #4	$141.52	11.715%	$158.0991	$158.10	$158.10	$158.10
Purchase #5	$190.72	12.163%	$213.9173	$213.92	$213.90	$213.90
Purchase #6	$27.39	4.504%	$28.6236	$28.62	$28.60	$28.60
Purchase #7	$164.60	7.264%	$176.5565	$176.56	$176.55	$176.60
7 purchase totals =	$985.34		$1,078.1044	$1,078.11	$1,078.10	$1,078.10