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	$110.72	13.137%	$125.2653	$125.27	$125.25	$125.30
Purchase #2	$90.71	12.149%	$101.7304	$101.73	$101.75	$101.70
Purchase #3	$153.88	13.139%	$174.0983	$174.10	$174.10	$174.10
Purchase #4	$35.56	7.520%	$38.2341	$38.23	$38.25	$38.20
Purchase #5	$70.38	10.196%	$77.5559	$77.56	$77.55	$77.60
Purchase #6	$33.31	9.516%	$36.4798	$36.48	$36.50	$36.50
Purchase #7	$80.99	6.460%	$86.222	$86.22	$86.20	$86.20
7 purchase totals =	$575.55		$639.5858	$639.59	$639.60	$639.60