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	$151.51	5.775%	$160.2597	$160.26	$160.25	$160.30
Purchase #2	$233.90	10.487%	$258.4291	$258.43	$258.45	$258.40
Purchase #3	$88.45	12.209%	$99.2489	$99.25	$99.25	$99.20
Purchase #4	$37.48	6.293%	$39.8386	$39.84	$39.85	$39.80
Purchase #5	$51.88	6.801%	$55.4084	$55.41	$55.40	$55.40
Purchase #6	$100.84	3.703%	$104.5741	$104.57	$104.55	$104.60
Purchase #7	$225.30	7.774%	$242.8148	$242.81	$242.80	$242.80
7 purchase totals =	$889.36		$960.5736	$960.57	$960.55	$960.50