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	$27.85	13.190%	$31.5234	$31.52	$31.50	$31.50
Purchase #2	$93.94	3.405%	$97.1387	$97.14	$97.15	$97.10
Purchase #3	$200.25	7.122%	$214.5118	$214.51	$214.50	$214.50
Purchase #4	$244.89	11.696%	$273.5323	$273.53	$273.55	$273.50
Purchase #5	$95.95	13.675%	$109.0712	$109.07	$109.05	$109.10
Purchase #6	$135.47	6.598%	$144.4083	$144.41	$144.40	$144.40
Purchase #7	$215.59	12.380%	$242.28	$242.28	$242.30	$242.30
7 purchase totals =	$1,013.94		$1,112.4657	$1,112.46	$1,112.45	$1,112.40