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	$160.45	6.750%	$171.2804	$171.28	$171.30	$171.30
Purchase #2	$208.83	6.673%	$222.7652	$222.77	$222.75	$222.80
Purchase #3	$14.87	5.582%	$15.7	$15.70	$15.70	$15.70
Purchase #4	$245.45	4.359%	$256.1492	$256.15	$256.15	$256.10
Purchase #5	$78.28	13.865%	$89.1335	$89.13	$89.15	$89.10
Purchase #6	$88.84	5.402%	$93.6391	$93.64	$93.65	$93.60
Purchase #7	$84.26	11.664%	$94.0881	$94.09	$94.10	$94.10
7 purchase totals =	$880.98		$942.7555	$942.76	$942.80	$942.70