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	$73.55	9.159%	$80.2864	$80.29	$80.30	$80.30
Purchase #2	$39.60	4.501%	$41.3824	$41.38	$41.40	$41.40
Purchase #3	$206.49	7.497%	$221.9706	$221.97	$221.95	$222.00
Purchase #4	$192.50	6.765%	$205.5226	$205.52	$205.50	$205.50
Purchase #5	$25.68	12.443%	$28.8754	$28.88	$28.90	$28.90
Purchase #6	$190.37	3.281%	$196.616	$196.62	$196.60	$196.60
Purchase #7	$243.70	9.738%	$267.4315	$267.43	$267.45	$267.40
7 purchase totals =	$971.89		$1,042.0849	$1,042.09	$1,042.10	$1,042.10