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	$37.77	13.867%	$43.0076	$43.01	$43.00	$43.00
Purchase #2	$62.71	3.701%	$65.0309	$65.03	$65.05	$65.00
Purchase #3	$218.48	9.482%	$239.1963	$239.20	$239.20	$239.20
Purchase #4	$84.47	5.429%	$89.0559	$89.06	$89.05	$89.10
Purchase #5	$49.49	7.180%	$53.0434	$53.04	$53.05	$53.00
Purchase #6	$156.51	5.729%	$165.4765	$165.48	$165.50	$165.50
Purchase #7	$98.55	5.293%	$103.7663	$103.77	$103.75	$103.80
7 purchase totals =	$707.98		$758.5769	$758.59	$758.60	$758.60