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	$83.50	7.642%	$89.8811	$89.88	$89.90	$89.90
Purchase #2	$156.97	10.168%	$172.9307	$172.93	$172.95	$172.90
Purchase #3	$230.78	3.345%	$238.4996	$238.50	$238.50	$238.50
Purchase #4	$170.56	6.168%	$181.0801	$181.08	$181.10	$181.10
Purchase #5	$181.90	11.543%	$202.8967	$202.90	$202.90	$202.90
Purchase #6	$171.41	4.341%	$178.8509	$178.85	$178.85	$178.90
Purchase #7	$115.70	6.358%	$123.0562	$123.06	$123.05	$123.10
7 purchase totals =	$1,110.82		$1,187.1953	$1,187.20	$1,187.25	$1,187.30