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	$60.36	3.867%	$62.6941	$62.69	$62.70	$62.70
Purchase #2	$200.92	10.633%	$222.2838	$222.28	$222.30	$222.30
Purchase #3	$76.82	8.330%	$83.2191	$83.22	$83.20	$83.20
Purchase #4	$103.56	7.614%	$111.4451	$111.45	$111.45	$111.40
Purchase #5	$26.90	4.256%	$28.0449	$28.04	$28.05	$28.00
Purchase #6	$38.27	11.555%	$42.6921	$42.69	$42.70	$42.70
Purchase #7	$102.37	6.269%	$108.7876	$108.79	$108.80	$108.80
7 purchase totals =	$609.20		$659.1667	$659.16	$659.20	$659.10