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	$157.37	12.801%	$177.5149	$177.51	$177.50	$177.50
Purchase #2	$45.40	10.653%	$50.2365	$50.24	$50.25	$50.20
Purchase #3	$149.25	4.808%	$156.4259	$156.43	$156.45	$156.40
Purchase #4	$232.58	9.414%	$254.4751	$254.48	$254.50	$254.50
Purchase #5	$207.79	5.157%	$218.5057	$218.51	$218.50	$218.50
Purchase #6	$91.40	13.293%	$103.5498	$103.55	$103.55	$103.50
Purchase #7	$40.52	5.570%	$42.777	$42.78	$42.80	$42.80
7 purchase totals =	$924.31		$1,003.4849	$1,003.50	$1,003.55	$1,003.40