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	$236.32	6.167%	$250.8939	$250.89	$250.90	$250.90
Purchase #2	$129.98	8.588%	$141.1427	$141.14	$141.15	$141.10
Purchase #3	$203.58	13.380%	$230.819	$230.82	$230.80	$230.80
Purchase #4	$152.69	6.373%	$162.4209	$162.42	$162.40	$162.40
Purchase #5	$63.42	3.171%	$65.431	$65.43	$65.45	$65.40
Purchase #6	$38.66	3.623%	$40.0607	$40.06	$40.05	$40.10
Purchase #7	$81.43	7.450%	$87.4965	$87.50	$87.50	$87.50
7 purchase totals =	$906.08		$978.2647	$978.26	$978.25	$978.20