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	$52.27	11.489%	$58.2753	$58.28	$58.30	$58.30
Purchase #2	$86.60	3.452%	$89.5894	$89.59	$89.60	$89.60
Purchase #3	$233.86	11.571%	$260.9199	$260.92	$260.90	$260.90
Purchase #4	$226.99	10.231%	$250.2133	$250.21	$250.20	$250.20
Purchase #5	$27.82	7.183%	$29.8183	$29.82	$29.80	$29.80
Purchase #6	$28.51	8.172%	$30.8398	$30.84	$30.85	$30.80
Purchase #7	$118.67	11.122%	$131.8685	$131.87	$131.85	$131.90
7 purchase totals =	$774.72		$851.5245	$851.53	$851.50	$851.50