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	$152.83	3.226%	$157.7603	$157.76	$157.75	$157.80
Purchase #2	$145.51	12.870%	$164.2371	$164.24	$164.25	$164.20
Purchase #3	$18.72	4.214%	$19.5089	$19.51	$19.50	$19.50
Purchase #4	$84.42	7.136%	$90.4442	$90.44	$90.45	$90.40
Purchase #5	$104.71	5.490%	$110.4586	$110.46	$110.45	$110.50
Purchase #6	$33.45	11.513%	$37.3011	$37.30	$37.30	$37.30
Purchase #7	$96.28	6.863%	$102.8877	$102.89	$102.90	$102.90
7 purchase totals =	$635.92		$682.5979	$682.60	$682.60	$682.60