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	$38.94	12.274%	$43.7195	$43.72	$43.70	$43.70
Purchase #2	$224.99	11.307%	$250.4296	$250.43	$250.45	$250.40
Purchase #3	$134.55	5.503%	$141.9543	$141.95	$141.95	$142.00
Purchase #4	$110.51	4.256%	$115.2133	$115.21	$115.20	$115.20
Purchase #5	$204.25	4.464%	$213.3677	$213.37	$213.35	$213.40
Purchase #6	$77.77	6.645%	$82.9378	$82.94	$82.95	$82.90
Purchase #7	$140.30	10.828%	$155.4917	$155.49	$155.50	$155.50
7 purchase totals =	$931.31		$1,003.1139	$1,003.11	$1,003.10	$1,003.10