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	$38.51	6.385%	$40.9689	$40.97	$40.95	$41.00
Purchase #2	$168.33	6.676%	$179.5677	$179.57	$179.55	$179.60
Purchase #3	$73.71	12.158%	$82.6717	$82.67	$82.65	$82.70
Purchase #4	$103.45	13.339%	$117.2492	$117.25	$117.25	$117.20
Purchase #5	$90.31	12.102%	$101.2393	$101.24	$101.25	$101.20
Purchase #6	$233.74	13.856%	$266.127	$266.13	$266.15	$266.10
Purchase #7	$59.72	9.405%	$65.3367	$65.34	$65.35	$65.30
7 purchase totals =	$767.77		$853.1605	$853.17	$853.15	$853.10