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	$249.56	11.464%	$278.1696	$278.17	$278.15	$278.20
Purchase #2	$88.53	6.718%	$94.4774	$94.48	$94.50	$94.50
Purchase #3	$137.37	12.454%	$154.4781	$154.48	$154.50	$154.50
Purchase #4	$172.62	13.821%	$196.4778	$196.48	$196.50	$196.50
Purchase #5	$72.90	4.770%	$76.3773	$76.38	$76.40	$76.40
Purchase #6	$142.76	3.797%	$148.1806	$148.18	$148.20	$148.20
Purchase #7	$159.51	12.143%	$178.8793	$178.88	$178.90	$178.90
7 purchase totals =	$1,023.25		$1,127.0401	$1,127.05	$1,127.15	$1,127.20