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	$17.41	7.755%	$18.7601	$18.76	$18.75	$18.80
Purchase #2	$72.77	12.114%	$81.5854	$81.59	$81.60	$81.60
Purchase #3	$135.70	6.823%	$144.9588	$144.96	$144.95	$145.00
Purchase #4	$90.65	11.285%	$100.8799	$100.88	$100.90	$100.90
Purchase #5	$184.67	13.435%	$209.4804	$209.48	$209.50	$209.50
Purchase #6	$55.52	4.488%	$58.0117	$58.01	$58.00	$58.00
Purchase #7	$155.69	5.450%	$164.1751	$164.18	$164.20	$164.20
7 purchase totals =	$712.41		$777.8514	$777.86	$777.90	$778.00