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	$99.73	9.561%	$109.2652	$109.27	$109.25	$109.30
Purchase #2	$128.59	11.437%	$143.2968	$143.30	$143.30	$143.30
Purchase #3	$24.95	10.271%	$27.5126	$27.51	$27.50	$27.50
Purchase #4	$231.84	7.617%	$249.4993	$249.50	$249.50	$249.50
Purchase #5	$88.29	8.203%	$95.5324	$95.53	$95.55	$95.50
Purchase #6	$11.63	5.692%	$12.292	$12.29	$12.30	$12.30
Purchase #7	$58.61	13.307%	$66.4092	$66.41	$66.40	$66.40
7 purchase totals =	$643.64		$703.8075	$703.81	$703.80	$703.80