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	$199.51	7.828%	$215.1276	$215.13	$215.15	$215.10
Purchase #2	$119.46	3.571%	$123.7259	$123.73	$123.75	$123.70
Purchase #3	$157.64	13.157%	$178.3807	$178.38	$178.40	$178.40
Purchase #4	$115.50	10.409%	$127.5224	$127.52	$127.50	$127.50
Purchase #5	$224.88	6.728%	$240.0099	$240.01	$240.00	$240.00
Purchase #6	$130.78	4.728%	$136.9633	$136.96	$136.95	$137.00
Purchase #7	$60.87	12.433%	$68.438	$68.44	$68.45	$68.40
7 purchase totals =	$1,008.64		$1,090.1678	$1,090.17	$1,090.20	$1,090.10