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	$153.59	9.387%	$168.0075	$168.01	$168.00	$168.00
Purchase #2	$120.71	13.873%	$137.4561	$137.46	$137.45	$137.50
Purchase #3	$174.81	11.510%	$194.9306	$194.93	$194.95	$194.90
Purchase #4	$73.46	5.591%	$77.5671	$77.57	$77.55	$77.60
Purchase #5	$240.44	4.150%	$250.4183	$250.42	$250.40	$250.40
Purchase #6	$141.43	7.199%	$151.6115	$151.61	$151.60	$151.60
Purchase #7	$150.62	9.720%	$165.2603	$165.26	$165.25	$165.30
7 purchase totals =	$1,055.06		$1,145.2514	$1,145.26	$1,145.20	$1,145.30