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	$184.51	3.700%	$191.3369	$191.34	$191.35	$191.30
Purchase #2	$229.29	11.249%	$255.0828	$255.08	$255.10	$255.10
Purchase #3	$96.32	5.779%	$101.8863	$101.89	$101.90	$101.90
Purchase #4	$59.87	10.613%	$66.224	$66.22	$66.20	$66.20
Purchase #5	$114.88	3.519%	$118.9226	$118.92	$118.90	$118.90
Purchase #6	$165.56	6.504%	$176.328	$176.33	$176.35	$176.30
Purchase #7	$34.87	12.392%	$39.1911	$39.19	$39.20	$39.20
7 purchase totals =	$885.30		$948.9717	$948.97	$949.00	$948.90