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	$83.53	7.448%	$89.7513	$89.75	$89.75	$89.80
Purchase #2	$246.61	11.758%	$275.6064	$275.61	$275.60	$275.60
Purchase #3	$161.68	3.140%	$166.7568	$166.76	$166.75	$166.80
Purchase #4	$59.82	9.666%	$65.6022	$65.60	$65.60	$65.60
Purchase #5	$163.65	9.358%	$178.9644	$178.96	$178.95	$179.00
Purchase #6	$137.48	11.134%	$152.787	$152.79	$152.80	$152.80
Purchase #7	$228.79	10.530%	$252.8816	$252.88	$252.90	$252.90
7 purchase totals =	$1,081.56		$1,182.3497	$1,182.35	$1,182.35	$1,182.50