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	$100.97	8.256%	$109.3061	$109.31	$109.30	$109.30
Purchase #2	$97.64	9.397%	$106.8152	$106.82	$106.80	$106.80
Purchase #3	$116.82	6.738%	$124.6913	$124.69	$124.70	$124.70
Purchase #4	$174.51	13.507%	$198.0811	$198.08	$198.10	$198.10
Purchase #5	$236.92	13.577%	$269.0866	$269.09	$269.10	$269.10
Purchase #6	$88.31	11.552%	$98.5116	$98.51	$98.50	$98.50
Purchase #7	$69.66	12.515%	$78.3779	$78.38	$78.40	$78.40
7 purchase totals =	$884.83		$984.8698	$984.88	$984.90	$984.90