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	$28.79	10.138%	$31.7087	$31.71	$31.70	$31.70
Purchase #2	$30.99	8.161%	$33.5191	$33.52	$33.50	$33.50
Purchase #3	$123.81	3.808%	$128.5247	$128.52	$128.50	$128.50
Purchase #4	$108.75	5.596%	$114.8357	$114.84	$114.85	$114.80
Purchase #5	$232.86	11.632%	$259.9463	$259.95	$259.95	$259.90
Purchase #6	$210.43	8.435%	$228.1798	$228.18	$228.20	$228.20
Purchase #7	$191.59	7.464%	$205.8903	$205.89	$205.90	$205.90
7 purchase totals =	$927.22		$1,002.6046	$1,002.61	$1,002.60	$1,002.50