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	$120.90	8.703%	$131.4219	$131.42	$131.40	$131.40
Purchase #2	$231.99	11.542%	$258.7663	$258.77	$258.75	$258.80
Purchase #3	$89.50	7.861%	$96.5356	$96.54	$96.55	$96.50
Purchase #4	$194.92	4.236%	$203.1768	$203.18	$203.20	$203.20
Purchase #5	$38.29	5.169%	$40.2692	$40.27	$40.25	$40.30
Purchase #6	$242.49	12.689%	$273.2596	$273.26	$273.25	$273.30
Purchase #7	$52.49	5.635%	$55.4478	$55.45	$55.45	$55.40
7 purchase totals =	$970.58		$1,058.8772	$1,058.89	$1,058.85	$1,058.90