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	$43.45	9.745%	$47.6842	$47.68	$47.70	$47.70
Purchase #2	$71.47	9.741%	$78.4319	$78.43	$78.45	$78.40
Purchase #3	$239.46	12.344%	$269.0189	$269.02	$269.00	$269.00
Purchase #4	$131.50	3.360%	$135.9184	$135.92	$135.90	$135.90
Purchase #5	$185.74	8.161%	$200.8982	$200.90	$200.90	$200.90
Purchase #6	$94.45	4.732%	$98.9194	$98.92	$98.90	$98.90
Purchase #7	$12.29	13.209%	$13.9134	$13.91	$13.90	$13.90
7 purchase totals =	$778.36		$844.7844	$844.78	$844.75	$844.70