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	$142.48	12.633%	$160.4795	$160.48	$160.50	$160.50
Purchase #2	$165.70	10.384%	$182.9063	$182.91	$182.90	$182.90
Purchase #3	$102.38	8.506%	$111.0884	$111.09	$111.10	$111.10
Purchase #4	$143.26	6.692%	$152.847	$152.85	$152.85	$152.80
Purchase #5	$72.63	11.574%	$81.0362	$81.04	$81.05	$81.00
Purchase #6	$74.40	10.835%	$82.4612	$82.46	$82.45	$82.50
Purchase #7	$14.94	7.592%	$16.0742	$16.07	$16.05	$16.10
7 purchase totals =	$715.79		$786.8928	$786.90	$786.90	$786.90