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	$82.28	7.601%	$88.5341	$88.53	$88.55	$88.50
Purchase #2	$77.67	3.700%	$80.5438	$80.54	$80.55	$80.50
Purchase #3	$90.37	10.452%	$99.8155	$99.82	$99.80	$99.80
Purchase #4	$198.50	5.571%	$209.5584	$209.56	$209.55	$209.60
Purchase #5	$158.53	8.209%	$171.5437	$171.54	$171.55	$171.50
Purchase #6	$69.72	11.851%	$77.9825	$77.98	$78.00	$78.00
Purchase #7	$210.61	12.755%	$237.4733	$237.47	$237.45	$237.50
7 purchase totals =	$887.68		$965.4513	$965.44	$965.45	$965.40