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	$6.98	10.576%	$7.7182	$7.72	$7.70	$7.70
Purchase #2	$123.54	12.708%	$139.2395	$139.24	$139.25	$139.20
Purchase #3	$218.61	7.310%	$234.5904	$234.59	$234.60	$234.60
Purchase #4	$132.96	6.872%	$142.097	$142.10	$142.10	$142.10
Purchase #5	$17.83	13.390%	$20.2174	$20.22	$20.20	$20.20
Purchase #6	$193.79	8.814%	$210.8707	$210.87	$210.85	$210.90
Purchase #7	$28.48	12.506%	$32.0417	$32.04	$32.05	$32.00
7 purchase totals =	$722.19		$786.7749	$786.78	$786.75	$786.70