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	$237.88	12.406%	$267.3914	$267.39	$267.40	$267.40
Purchase #2	$82.74	12.754%	$93.2927	$93.29	$93.30	$93.30
Purchase #3	$119.83	3.690%	$124.2517	$124.25	$124.25	$124.30
Purchase #4	$223.41	5.504%	$235.7065	$235.71	$235.70	$235.70
Purchase #5	$167.32	9.307%	$182.8925	$182.89	$182.90	$182.90
Purchase #6	$34.43	13.779%	$39.1741	$39.17	$39.15	$39.20
Purchase #7	$56.68	9.200%	$61.8946	$61.89	$61.90	$61.90
7 purchase totals =	$922.29		$1,004.6035	$1,004.59	$1,004.60	$1,004.70