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	$138.69	7.117%	$148.5606	$148.56	$148.55	$148.60
Purchase #2	$209.53	9.506%	$229.4479	$229.45	$229.45	$229.40
Purchase #3	$143.29	12.164%	$160.7198	$160.72	$160.70	$160.70
Purchase #4	$188.78	4.154%	$196.6219	$196.62	$196.60	$196.60
Purchase #5	$164.77	13.407%	$186.8607	$186.86	$186.85	$186.90
Purchase #6	$95.57	12.784%	$107.7877	$107.79	$107.80	$107.80
Purchase #7	$46.35	9.216%	$50.6216	$50.62	$50.60	$50.60
7 purchase totals =	$986.98		$1,080.6202	$1,080.62	$1,080.55	$1,080.60