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	$29.66	4.656%	$31.041	$31.04	$31.05	$31.00
Purchase #2	$79.67	3.389%	$82.37	$82.37	$82.35	$82.40
Purchase #3	$132.90	6.423%	$141.4362	$141.44	$141.45	$141.40
Purchase #4	$201.45	6.739%	$215.0257	$215.03	$215.05	$215.00
Purchase #5	$232.82	10.335%	$256.8819	$256.88	$256.90	$256.90
Purchase #6	$146.71	6.612%	$156.4105	$156.41	$156.40	$156.40
Purchase #7	$193.87	3.871%	$201.3747	$201.37	$201.35	$201.40
7 purchase totals =	$1,017.08		$1,084.5400	$1,084.54	$1,084.55	$1,084.50