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	$82.73	10.744%	$91.6185	$91.62	$91.60	$91.60
Purchase #2	$47.96	7.445%	$51.5306	$51.53	$51.55	$51.50
Purchase #3	$181.70	10.466%	$200.7167	$200.72	$200.70	$200.70
Purchase #4	$219.84	13.470%	$249.4524	$249.45	$249.45	$249.50
Purchase #5	$191.36	8.632%	$207.8782	$207.88	$207.90	$207.90
Purchase #6	$98.28	11.860%	$109.936	$109.94	$109.95	$109.90
Purchase #7	$95.53	8.786%	$103.9233	$103.92	$103.90	$103.90
7 purchase totals =	$917.40		$1,015.0557	$1,015.06	$1,015.05	$1,015.00