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	$28.63	9.858%	$31.4523	$31.45	$31.45	$31.50
Purchase #2	$232.91	8.850%	$253.5225	$253.52	$253.50	$253.50
Purchase #3	$54.71	12.667%	$61.6401	$61.64	$61.65	$61.60
Purchase #4	$193.99	11.304%	$215.9186	$215.92	$215.90	$215.90
Purchase #5	$147.69	4.335%	$154.0924	$154.09	$154.10	$154.10
Purchase #6	$225.53	13.700%	$256.4276	$256.43	$256.45	$256.40
Purchase #7	$70.34	9.342%	$76.9112	$76.91	$76.90	$76.90
7 purchase totals =	$953.80		$1,049.9647	$1,049.96	$1,049.95	$1,049.90