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	$250.56	7.384%	$269.0614	$269.06	$269.05	$269.10
Purchase #2	$45.28	3.576%	$46.8992	$46.90	$46.90	$46.90
Purchase #3	$88.96	12.201%	$99.814	$99.81	$99.80	$99.80
Purchase #4	$98.96	13.277%	$112.0989	$112.10	$112.10	$112.10
Purchase #5	$159.87	13.661%	$181.7098	$181.71	$181.70	$181.70
Purchase #6	$133.43	7.132%	$142.9462	$142.95	$142.95	$142.90
Purchase #7	$105.80	12.541%	$119.0684	$119.07	$119.05	$119.10
7 purchase totals =	$882.86		$971.5979	$971.60	$971.55	$971.60