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	$138.73	11.809%	$155.1126	$155.11	$155.10	$155.10
Purchase #2	$89.79	6.723%	$95.8266	$95.83	$95.85	$95.80
Purchase #3	$53.59	10.746%	$59.3488	$59.35	$59.35	$59.30
Purchase #4	$35.37	11.268%	$39.3555	$39.36	$39.35	$39.40
Purchase #5	$75.37	6.666%	$80.3942	$80.39	$80.40	$80.40
Purchase #6	$117.46	8.640%	$127.6085	$127.61	$127.60	$127.60
Purchase #7	$177.69	13.783%	$202.181	$202.18	$202.20	$202.20
7 purchase totals =	$688.00		$759.8272	$759.83	$759.85	$759.80