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	$72.47	13.856%	$82.5114	$82.51	$82.50	$82.50
Purchase #2	$171.80	11.189%	$191.0227	$191.02	$191.00	$191.00
Purchase #3	$139.70	3.638%	$144.7823	$144.78	$144.80	$144.80
Purchase #4	$174.86	5.230%	$184.0052	$184.01	$184.00	$184.00
Purchase #5	$42.66	5.227%	$44.8898	$44.89	$44.90	$44.90
Purchase #6	$29.33	12.820%	$33.0901	$33.09	$33.10	$33.10
Purchase #7	$135.26	5.288%	$142.4125	$142.41	$142.40	$142.40
7 purchase totals =	$766.08		$822.7140	$822.71	$822.70	$822.70