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	$156.53	7.774%	$168.6986	$168.70	$168.70	$168.70
Purchase #2	$46.54	13.568%	$52.8545	$52.85	$52.85	$52.90
Purchase #3	$228.89	4.669%	$239.5769	$239.58	$239.60	$239.60
Purchase #4	$204.96	5.499%	$216.2308	$216.23	$216.25	$216.20
Purchase #5	$181.84	5.520%	$191.8776	$191.88	$191.90	$191.90
Purchase #6	$6.80	9.410%	$7.4399	$7.44	$7.45	$7.40
Purchase #7	$28.83	9.321%	$31.5172	$31.52	$31.50	$31.50
7 purchase totals =	$854.39		$908.1955	$908.20	$908.25	$908.20