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	$247.97	8.437%	$268.8912	$268.89	$268.90	$268.90
Purchase #2	$180.35	5.824%	$190.8536	$190.85	$190.85	$190.90
Purchase #3	$181.43	12.158%	$203.4883	$203.49	$203.50	$203.50
Purchase #4	$25.93	5.464%	$27.3468	$27.35	$27.35	$27.30
Purchase #5	$180.72	4.662%	$189.1452	$189.15	$189.15	$189.10
Purchase #6	$72.41	11.420%	$80.6792	$80.68	$80.70	$80.70
Purchase #7	$130.34	7.218%	$139.7479	$139.75	$139.75	$139.70
7 purchase totals =	$1,019.15		$1,100.1522	$1,100.16	$1,100.20	$1,100.10