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	$74.53	5.488%	$78.6202	$78.62	$78.60	$78.60
Purchase #2	$91.25	8.185%	$98.7188	$98.72	$98.70	$98.70
Purchase #3	$62.82	3.170%	$64.8114	$64.81	$64.80	$64.80
Purchase #4	$225.99	7.408%	$242.7313	$242.73	$242.75	$242.70
Purchase #5	$29.93	5.287%	$31.5124	$31.51	$31.50	$31.50
Purchase #6	$176.31	8.715%	$191.6754	$191.68	$191.70	$191.70
Purchase #7	$7.51	4.247%	$7.8289	$7.83	$7.85	$7.80
7 purchase totals =	$668.34		$715.8984	$715.90	$715.90	$715.80