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	$105.65	8.185%	$114.2975	$114.30	$114.30	$114.30
Purchase #2	$101.97	7.782%	$109.9053	$109.91	$109.90	$109.90
Purchase #3	$116.44	12.701%	$131.229	$131.23	$131.25	$131.20
Purchase #4	$250.56	9.328%	$273.9322	$273.93	$273.95	$273.90
Purchase #5	$136.74	5.447%	$144.1882	$144.19	$144.20	$144.20
Purchase #6	$136.48	4.396%	$142.4797	$142.48	$142.50	$142.50
Purchase #7	$5.87	10.356%	$6.4779	$6.48	$6.50	$6.50
7 purchase totals =	$853.71		$922.5098	$922.52	$922.60	$922.50